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  • 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
  • Catalysis
  • Wiley-Blackwell  (152)
  • American Chemical Society (ACS)
  • American Physical Society
  • Cell Press
  • MDPI Publishing
  • Springer Science + Business Media
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  • 1
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    Hydroxyapatite catalyzed hydrothermal liquefaction transforms food waste from an environmental liability to renewable fuel (2023)
    Cell Press
    Details
    Publication Date: 2023-03-08
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in LeClerc, H., Tompsett, G., Paulsen, A., McKenna, A., Niles, S., Reddy, C., Nelson, R., Cheng, F., Teixeira, A., & Timko, M. Hydroxyapatite catalyzed hydrothermal liquefaction transforms food waste from an environmental liability to renewable fuel. IScience, 25(9), (2022): 104916, https://doi.org/10.1016/j.isci.2022.104916.
    Description: Food waste is an abundant and inexpensive resource for the production of renewable fuels. Biocrude yields obtained from hydrothermal liquefaction (HTL) of food waste can be boosted using hydroxyapatite (HAP) as an inexpensive and abundant catalyst. Combining HAP with an inexpensive homogeneous base increased biocrude yield from 14 ± 1 to 37 ± 3%, resulting in the recovery of 49 ± 2% of the energy contained in the food waste feed. Detailed product analysis revealed the importance of fatty-acid oligomerization during biocrude formation, highlighting the role of acid-base catalysts in promoting condensation reactions. Economic and environmental analysis found that the new technology has the potential to reduce US greenhouse gas emissions by 2.6% while producing renewable diesel with a minimum fuel selling price of $1.06/GGE. HAP can play a role in transforming food waste from a liability to a renewable fuel.
    Description: This work was funded by the DOE Bioenergy Technology Office (DE-EE0008513), a DOE DBIR (DE-SC0015784) and the MassCEC. The authors thank WenWen Yao, Department of Environmental Science at WPI, for TOC analysis, Mainstream Engineering for heating value characterization of the oil and solid samples, Wei Fan for assistance in obtaining SEM images and, Julia Martin and Ronald Grimm for their assistance in collecting XPS data, and Jeffrey R. Page for his assistance with oil upgrading and analysis. HOL was partially funded for this work by NSF Graduate Research Fellowship award number 2038257. A portion of this work was performed at the National High Magnetic Field Laboratory Ion Cyclotron Resonance user facility, which is supported by the NSF Division of Materials Research and Division of Chemistry through DMR 16-44779 and the State of Florida.
    Keywords: Chemistry ; Chemical engineering ; Catalysis
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Comment on ‘Magnitude conversion problem using general orthogonal regression’ by H. R. Wason, Ranjit Das and M. L. Sharma, (Geophys. J. Int., 190, 1091–1096) (2015)
    Wiley-Blackwell
    In:  Magnitude conversion problem using general orthogonal regression’ by H. R. Wason, Ranjit Das and M. L. Sharma, (Geophys. J. Int., 190, 1091–1096)
    Details
    Publication Date: 2017-04-04
    Description: The argument proposed by Wason et al. that the conversion of magnitudes from a scale (e.g. Ms or mb) to another (e.g. Mw), using the coefficients computed by the general orthogonal regression method (Fuller) is biased if the observed values of the predictor (independent) variable are used in the equation as well as the methodology they suggest to estimate the supposedly true values of the predictor variable are wrong for a number of theoretical and empirical reasons. Hence, we advise against the use of such methodology for magnitude conversions.
    Description: Published
    Description: 626-627
    Description: 3T. Pericolosità sismica e contributo alla definizione del rischio
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake source observations ; Statistical seismology ; Computational seismology ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Are the source models of the M7.1 1908 Messina Straits earthquake reliable? Insights from a novel inversion and a sensitivity analysis of levelling data (2013)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: For decades, many authors have attempted to define the location, geometry and kinematics of the causative fault for the 1908 December 28, M 7.1 earthquake that struck the Messina Straits between Sicily and Calabria (southern Italy). The coseismic displacement caused a predominant downwarping of the Straits and small land uplift away from it, which were documented by levelling surveys performed 1 yr before and immediately after the earthquake. Most of the source models based on inversion of levelling data suggested that the earthquake was caused by a low angle, east-dipping blind normal fault, whose upper projection intersects the Earth surface on the Sicilian (west) side of the Messina Straits.An alternative interpretation holds that the causative fault is one of the high-angle, west-dipping faults located in southern Calabria, on the eastern side of the Straits, and may in large part coincide with the mapped Armo Fault. Here, we critically review the levelling data with the aim of defining both their usefulness and limits in modelling the seismogenic fault. We demonstrate that the levelling data alone are not capable of discriminating between the two oppositely dipping fault models, and thus their role as a keystone for modellers is untenable. However, new morphotectonic and geodetic data indicate that the Armo Fault has very recent activity and is accumulating strain. The surface observations, together with appraisal ofmacroseismic intensity distribution, available seismic tomography and marine geophysical evidence, lends credit to the hypothesis that the Armo and possibly the S. Eufemia faults are part of a major crustal structure that slipped during the 1908 earthquake.
    Description: Published
    Description: 1025-1041
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake source ; Messina Straits ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    A comparison of moment magnitude estimates for the European–Mediterranean and Italian regions (2013)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: With the goal of constructing a homogeneous data set of moment magnitudes (Mw) to be used for seismic hazard assessment, we compared Mw estimates from moment tensor catalogues available online. We found an apparent scaling disagreement between Mw estimates from the National Earthquake Information Center (NEIC) of the US Geological Survey and from the Global Centroid Moment Tensor (GCMT) project. We suspect that this is the effect of an underestimation ofMw 〉 7.0 (M0 〉 4.0 × 1019 Nm) computed by NEIC owing to the limitations of their computational approach. We also found an apparent scaling disagreement between GCMT and two regional moment tensor catalogues provided by the ‘Eidgen¨ossische Technische Hochschule Z¨urich’ (ETHZ) and by the European–Mediterranean Regional Centroid Moment Tensor (RCMT) project of the Italian ‘Istituto Nazionale di Geofisica e Vulcanologia’ (INGV). This is probably the effect of the overestimation of Mw 〈 5.5 (M0 〈 2.2 × 1017 Nm), up to year 2002, and of Mw 〈 5.0 (M0 〈 4.0 × 1016 Nm), since year 2003, owing to the physical limitations of the standard CMT inversion method used by GCMT for the earthquakes of relatively low magnitude. If the discrepant data are excluded from the comparisons, the scaling disagreements become insignificant in all cases. We observed instead small absolute offsets (≤0.1 units) for NEIC and ETHZ catalogues with respect to GCMT whereas there is an almost perfect correspondence between RCMT and GCMT. Finally, we found a clear underestimation of about 0.2 units of Mw magnitudes computed at the INGV using the time-domain moment tensor (TDMT) method with respect to those reported by GCMT and RCMT. According to our results, we suggest appropriate offset corrections to be applied to Mw estimates from NEIC, ETHZ and TDMT catalogues before merging their data with GCMT and RCMT catalogues. We suggest as well to discard the probably discrepant data from NEIC and GCMT if other Mw estimates from different sources are available for the same earthquakes. We also estimate approximately the average uncertainty of individual Mw estimates to be about 0.07 magnitude units for the GCMT, NEIC, RCMT and ETHZ catalogues and about 0.13 for the TDMT catalogue.
    Description: European Union research project SHARE (Seismic Hazard Harmonization in Europe), within the ambit of Task 3.1 ‘European Earthquake Database’
    Description: Published
    Description: 1733-1745
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake source observations; Statistical seismology ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Some insights on the occurrence of recent volcanic eruptions of Mount Etna volcano (Sicily, Italy) (2012)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-03
    Description: In the first part of this work, we make use of two non-parametric statistical pattern recognition algorithms and a multiple regression analysis to analyse seismic clusters occur ring around Mount Etna, Italy. The aim is to determine if the onset of flank eruptions at Mount Etna is linked to variations in the regional seismicity at a timescale of few weeks. From the analysis, we find that the discrimination between clusters preceding flank eruptions and clusters not related in time to flank activity is mainly linked to the volume output of the previous flank eruption, in some cases together with the time elapsed from its end. Instead, we do not find any difference in the seismicity features characterizing different types of clusters, except for a very small contribution of the number of seismic events in the clusters. This result does not confirm the existence, suggested in the past, of a direct link between the regional state of stress at a timescale of few weeks and the occurrence of flank eruptions on Mount Etna volcano. On the contrary, the result suggests that a prominent role in the flank eruption occur rence is played by the re-charging of the feeding system. In the second part of this study we analyse the relationship between the magma volume erupted in an eruption and the interevent time following it, finding that a ‘time-predictable model’ satisfactorily describes the occurrence of eruptions at Mount Etna in the last decades. The latter analysis is car ried out both on the flank eruption catalogue only, and on the complete catalogue of flank and summit eruptions, with comparable results.
    Description: Published
    Description: 1203–1218
    Description: JCR Journal
    Description: restricted
    Keywords: flank eruptions ; Mount Etna volcano ; regional tectonic stress ; statistical pattern recognition ; time predictability ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    Crustal heterogeneity highlighted by spatial b-value map in theWellington region of New Zealand (2010)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: We map the b-value in the subduction zone of theWellington region, NewZealand, using a high quality earthquake catalogue relocated with a 3-D seismic velocity model, consisting of 50 314 events that occurred between 1990 and 2005. In order to investigate heterogeneity in the crust of the overlying plate and in the upper plane of the Wadati–Benioff Zone (WBZ), we analyse a series of cross-sections perpendicular to the strike of the subduction zone. We calculate the b-values selecting events with magnitude of completeness ≥2.4 and depth ≤65 km and projecting the seismicity within 20 km on each side of the cross-sectional planes. We observe areas of high b-value (∼1.7) near the plate interface and regions of low b-value anomalies are detected both in the WBZ in the northwest region below 40 km depth and in the overlying plate in the northern South Island at 10 km depth. The anomalies are statistically significant based on Utsu’s p-test and the bootstrap method and are not data processing method or parameter dependent. We compare the b-value distribution with previously determined 3-D distributions of Vp, Vp/Vs andQp from seismic tomography. This comparison suggests that material inhomogeneity, caused by fluid filled cracks resulting from dehydration of the subducted slab and subducted sediments, is the predominant cause of b-value variation in the shallow part of this subduction zone. Our observations are consistent with a previously proposed conceptual model that fluid distribution in the shallow part of this subduction zone is controlled by the permeability of geological terranes in the overlying plate.
    Description: Published
    Description: 451-460
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Seismic attenuation ; Seismic tomography ; Statistical seismology ; Subduction zone processes ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
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    Analysis of self-organised criticality in the Olami-Feder-Christensen model and in real earthquakes (2007)
    American Physical Society
    Details
    Publication Date: 2017-04-04
    Description: We perform an analysis on the dissipative Olami-Feder-Christensen model on a small world topology considering avalanche size differences. We show that when criticality appears, the probability density functions (PDFs) for the avalanche size differences at different times have fat tails with a q-Gaussian shape. This behavior does not depend on the time interval adopted and is found also when considering energy differences between real earthquakes. Such a result can be analytically understood if the sizes (released energies) of the avalanches (earthquakes) have no correlations. Our findings support the hypothesis that a self-organized criticality mechanism with long-range interactions is at the origin of seismic events and indicate that it is not possible to predict the magnitude of the next earthquake knowing those of the previous ones.
    Description: Published
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: SOC, earthquakes interaction ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
    Electronic Resource
    Electronic Resource
    Nickel- and Palladium-Catalyzed Cross-Coupling Reactions at the Bridgehead of Bicyclo[1.1.1]pentane Derivatives - A Convenient Access to Liquid Crystalline Compounds Containing Bicyclo[1.1.1]pentane Moieties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1137-1155 
    Details
    ISSN: 1434-193X
    Keywords: Bicyclo[1.1.1]pentane ; Haloarenes, cross-coupling of ; Propellanes ; Palladium ; Catalysis ; Small-ring systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Radical addition reactions of organyl iodides 7a-s onto [1.1.1]propellane (2) followed by halogen-lithium exchange and transmetallation with zinc chloride, as well as additions of Grignard reagents to 2, have furnished a variety of 3-substituted bicyclo[1.1.1]pentyl-1-magnesium (14) and -zinc (19) derivatives. The latter have been coupled with various alkenyl, aryl, and biaryl halides and triflates under NiCl2dppe, Pd(PPh3)4, or PdCl2(dppf) catalysis to give a number of 1,3-disubstituted bicyclo[1.1.1]pentyl derivatives 17, 20, and 23, several of which exhibit liquid crystalline properties, in moderate to very good yields. The coupling products 20ca, 23ab, 23ae, 23ff, and 23fg have been further transformed to yield bicyclo[1.1.1]pentyl derivatives 32, 24ab, 24ae, 27ff, and 27fg, respectively, bearing alkynyl, cyano, and/or alkenyl groups.
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  • 9
    Electronic Resource
    Electronic Resource
    Construction of Quaternary Stereocenters by Nickel-Catalysis of Asymmetric Michael Reactions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 701-705 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric catalysis ; Catalysis ; Addition reactions ; N ligands ; Nickel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Quaternary stereocenters were constructed with an enantioselectivity of up to 91% ee under aerobic conditions and at ambient temperature in the Michael reaction of β-dicarbonyl compounds and methyl vinyl ketone with Ni(OAc)2·4H2O and optically active trans-1,2-diaminocyclohexane as a chiral catalyst.
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  • 10
    Electronic Resource
    Electronic Resource
    Selective and Environmentally Benign Aerobic Catalytic Oxidation of Alcohols by a Molybdenum-Copper System (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 655-658 
    Details
    ISSN: 1434-1948
    Keywords: Molybdenum ; Copper ; Oxidation ; Alcohols ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of activated primary and secondary alcohols to the corresponding aldehydes and ketones can be carried out with molecular oxygen, in the presence of the bimetallic molybdenum-copper system MoO2(acac)2-Cu(NO3)2 as catalyst.
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  • 11
    Electronic Resource
    Electronic Resource
    New Methodologies Based on Arene-Catalyzed Lithiation Reactions and Their Application to Synthetic Organic Chemistry (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 225-237 
    Details
    ISSN: 1434-193X
    Keywords: Lithium ; Arenes ; Catalysis ; Organolithium ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The applications of arene-catalyzed lithiation reactions during recent years are reviewed. This methodology has been used to obtain functionalized organolithium compounds from halogenated as well as nonhalogenated materials, such as heterocycles, sulfones, triflates, ethers, thioethers, amides, and esters. This arene-catalyzed lithiation has also been used in the preparation of polylithiated intermediates. Sub-stoichiometric amounts of the arene may be supported on a polymeric material, its catalytic activity being as efficient as in the solution version.
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  • 12
    Electronic Resource
    Electronic Resource
    A Two-Step Palladium-Catalyzed Coupling Scheme for the Synthesis of Ferrocene-Labeled Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    Details
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
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  • 13
    Electronic Resource
    Electronic Resource
    New Insights into the Mechanism of Hydroperoxide Activation by Investigation of Dynamic Processes in the Coordination Sphere of Seven-Coordinated Molybdenum Peroxo Complexes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1107-1114 
    Details
    ISSN: 1434-1948
    Keywords: Catalysis ; Densitiy functional theory ; Epoxidation ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven-coordinated molybdenum oxobisperoxo complexes with chelate nitrogen donors like pyrazolylpyridines are catalysts for the epoxidation of olefins. An NMR spectroscopic and quantumchemical study on the fluxionality of the chelate ligand proves that during this process partial ligand dissociation takes place. This gave rise to a detailed theoretical study on the activation of CH3OOH at the model complex (NH3)2MoO(O2)2 including dissociation of one of the ammonia ligands and proton transfer from the hydroperoxide to one of the peroxo ligands.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99429_s.pdf or from the author.
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  • 14
    Electronic Resource
    Electronic Resource
    Palladium(0) Complexes of a 15-Membered Macrocyclic Triolefin as a Recoverable Catalyst - Monomer- and Polystyrene-Anchored Versions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 239-243 
    Details
    ISSN: 1434-193X
    Keywords: Macrocycles ; Palladium ; Polymers ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Preparation of the 15-membered cycle (E,E,E)-1,6,11-tris[(2,4,6-triisopropylphenyl)sulfonyl]-1,6,11-triazacyclopentadeca3,8,13-triene (8) is reported. This cyclic triolefin forms a stable Pd0 complex 9 which catalyzes several cross-coupling reactions and can be recovered. Anchoring to a polystyrene framework affords a solid version of the catalyst, which is recovered by simple filtration and reused without loss of catalytic activity.
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  • 15
    Electronic Resource
    Electronic Resource
    Synthesis of 1β-Methylcarbapenem Antibiotic Precursors by Cyclization Using π-Allylpalladium Complexes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 621-626 
    Details
    ISSN: 1434-193X
    Keywords: 1β-Methylcarbapenems ; Palladium ; Ruthenium ; Catalysis ; Cyclizations ; Stereoselective hydrogenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -An efficient diastereoselective multi-step synthesis of bicyclic 1β-methylcarbapenem antibiotic precursors has been developed, starting from the commercially available 4-acetoxyazetidin-2-one 4. Chiral ruthenium catalysts are used in the hydrogenation step to control the β-stereochemistry at the 1-position, and a π-allylpalladium ring-closure strategy is used to form the functionalized carbapenem skeleton.
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  • 16
    Electronic Resource
    Electronic Resource
    Palladium-Catalyzed Cyclocarbonylation of o-Ethynylphenols and Vinyl Triflates To Form 3-Alkylidene-2-coumaranones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1137-1141 
    Details
    ISSN: 1434-193X
    Keywords: Cyclocarbonylation ; Alkynes ; Catalysis ; Palladium ; Vinyl triflates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -o-Ethynylphenols react with vinyl triflates, in the presence of tetrakis(triphenylphosphane)palladium(0) and under carbon monoxide, to form 3-alkylidene-2-coumaranones in good yield.
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  • 17
    Electronic Resource
    Electronic Resource
    New Chiral Catalysts Containing N,O-Heterocycles Derived from Chiral Amino Alcohols (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3323-3333 
    Details
    ISSN: 1434-193X
    Keywords: Chirality ; Catalysis ; Amino acids ; Crown ethers ; Heterocyclic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselectivity exerted by a new series of chiral catalysts containing N,O-heterocycles of different sizes has been checked in the addition of diethylzinc to benzaldehyde, which was used as a model reaction. The catalysts were derived from natural amino acids, following a relatively simple procedure, and in several cases excellent ee values were obtained. The results were complementary since ee's ranged from 98% (R) to 94% (S) excesses of the final 1-phenylpropan-1-ol. Molecular mechanics calculations suggested that the production of the R alcohol may be explained by a mechanism similar to that described by Noyori, in which ZnEt2 interacts solely with the N-C-C-OH fragment, whereas the formation of the S enantiomer needed the direct participation of the lateral chain of the parent amino acid and the N,O-heterocycle.
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  • 18
    Electronic Resource
    Electronic Resource
    Cerium(III) Chloride Catalyzed Michael Reaction of 1,3-Dicarbonyl Compounds and Enones in the Presence of Sodium Iodide Under Solvent-Free Conditions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 617-620 
    Details
    ISSN: 1434-193X
    Keywords: Cerium(III) chloride heptahydrate ; Catalysis ; 1,3-Dicarbonyl compounds ; Enones ; Michael reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Cerium(III) chloride heptahydrate in the presence of sodium iodide catalyses the Michael addition of 1,3-dicarbonyl compounds to α,β-unsaturated ketones and α,β-unsaturated aldehydes with extraordinary efficiency. The very mild conditions allow high chemoselectivity as shown by the absence of the typical side reactions, which can be observed in the conventional base-catalyzed processes. More interestingly, when at least one of the starting materials is liquid at room temperature, the reaction can also be performed without solvents. The CeCl3· 7 H2O/NaI catalyst system can be easily separated from the reaction mixture and it can be reused without an appreciable loss of activity. Advantages of the present procedure, which utilizes cheap and “friendly” reagents, over the previously reported ones, are discussed.
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  • 19
    Electronic Resource
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    Synthesis of γ-Amino- and δ-Amino-Functionalised Ethers, Amines, or Silanes by Hydroaminomethylation of Heterofunctionalised Allylic Compounds (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 653-660 
    Details
    ISSN: 1434-193X
    Keywords: Hydroaminomethylation ; Rhodium ; Catalysis ; Carbonylation ; Heterofunctionalised allylic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Heterofunctionalised allylic ethers 1, silanes 5, and amines 9 are hydroformylated in the presence of primary or secondary amines 2 to form the corresponding γ-amino- and δ-amino-functionalised compounds. The rhodium(I)-catalysed reaction sequence proceeds by aldehyde formation and subsequent reductive amination to generate the corresponding functionalised secondary or tertiary amines. This selective one-pot hydroaminomethylation procedure establishes access to γ-amino- and δ-amino-functionalised ethers, amines or silanes with potential biological activity.
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    Synthesis of γ-Butyrolactones by a Baeyer-Villiger Oxidation with Hydrogen Peroxide, Catalysed by Methyltrioxorhenium (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1767-1770 
    Details
    ISSN: 1434-193X
    Keywords: Baeyer-Villiger reaction ; Lactones ; Methyltrioxorhenium ; Catalysis ; Oxidations ; Cyclobutanones ; Ketones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: γ-Butyrolactones were obtained in good yields and high regioselectivity by a Baeyer-Villiger oxidation with H2O2 catalysed by methyltrioxorhenium. The lactonization was chemoselective in the presence of double bonds, aromatic rings, and chlorine substituents. A trimethylsiloxy-substituted ketone was converted directly into a hydroxylated lactone in good yield and regioselectively.
    Additional Material: 1 Tab.
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  • 21
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    Small Libraries of Polymer-Supported Amino Alcohols: An Application to the Enantioselective Reduction of Acetophenone by LAH (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2263-2267 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohols ; Polymers ; Enantioselective reagents ; Catalysis ; Merrifield resins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from simple amino acid esters and Merrifield resins, a small library of polymer-bound chiral-β-amino alcohols can be prepared. By reaction with LiALH4 the corresponding chiral reducing agents are obtained, having structural variations at both the α and β positions. All supported reagents are able to reduce acetophenone to 1-phenylethanol. Enantioselectivity is observed when the steric hindrance in the chiral fragment is increased. Best results are obtained for the supported derivative of α,α-diphenyl phenylalaninol.
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    New Hydrogen Transfer Catalysts (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2219-2230 
    Details
    ISSN: 1434-193X
    Keywords: Retrodisproportionation ; Arenes ; EPR spectroscopy ; Thermochemistry ; Coal liquefaction ; Catalysis ; Hydrogen transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transfer of hydrogen from excess 9,10-dihydroanthracene (DHA) to acceptors such as α-methylstyrene is catalyzed, i.e. occurs at temperatures in the range 200-260 °C instead of 280-320 °C, when hydrocarbons with weaker C-H bonds than DHA, e.g. 6H-benzo[cd]pyrene (4), 7H-dibenzo[a,kl]anthracene (5), 4-methyl-7H-benzo[de]naphthacene (6) or 8H-dibenzo[b,fg]pyrene (7), are added to the reaction mixture. The reactions are initiated by bimolecular H-atom transfer from 4-7 to the acceptor (retrodisproportionation) and proceed by nonchain radical mechanisms. This is supported by isotopic labelling and kinetic isotope effects, substituent and solvent effects, EPR spectroscopy of intermediate radicals, and by a comparison of the thermochemical and kinetic characteristics of these reactions.
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    Vinyl- and Divinylcyclopentadienes by Rhodium-Catalyzed Condensation of Alkynes with Cross-Conjugated Amino Metallahexatrienes [= (1-Amino-1,3-butadien-2-yl)carbene Complexes] (M = Cr, W) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2545-2561 
    Details
    ISSN: 1434-193X
    Keywords: Carbene complexes ; Catalysis ; Metallahexatrienes ; Vinyl cyclopentadienes ; Transmetallation ; Rhodium ; Tungsten ; Chromium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report on the first example of a transition metal-catalyzed cyclization reaction of a Fischer carbene complex. It comprises the generation of vinyl- and divinyl cyclopentadienes under exceedingly mild conditions at 20 °C by condensation of (1-amino-1,3-butadien-2-yl)carbene complexes (= cross-conjugated metallahexatrienes) (CO)5M=C(OEt)C(=CHNR2)CR1=CHR23 (M = Cr, W) with alkynes R3C≡CH 4 (R3 = Ph, cyclohex-1-enyl, isopropenyl, methoxymethyl, 1-trimethylsiloxycyclohex-1-yl) in the presence of catalytic amounts of [(COD)RhCl]2. The starting compounds 3 are accessible in high yields by addition of enamines (E)-R2NCH=CHR22 to (1-alkynyl)carbene complexes (CO)5M=C(OEt)C≡CR11 (M = Cr, W; R1 = Ph, cyclohex-1-enyl).
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    A New Access to Diarylmaleic Anhydrides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1421-1426 
    Details
    ISSN: 1434-193X
    Keywords: Anhydrides ; Coupling reaction ; Enols ; Palladium ; Tin ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new three-step synthesis of diarylmaleic anhydrides 6, starting from 3-aryl-2-hydroxybut-2-enedioates 2, is reported.
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    Electronic Effects on the Stereoselectivity of Epoxidation Reactions Catalysed by Manganese Porphyrins (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3281-3286 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Epoxidation ; Manganese ; Porphyrins ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of MnIII porphyrins progressively halogenated in the β-pyrrolic positions was employed to catalyse the epoxidation of cis-stilbene by iodosylbenzene, and to study the role of the electronic effects on the stereoselectivity of this process. A gradual improvement in the stereoselectivity on increasing the number of β-halogen atoms was observed. The role of steric effects upon the epoxidation was also investigated by placing ortho-substituents in the meso-phenyl rings, and it was found that steric effects are more important than electronic effects toward the stereoselectivity of this process. These results can be rationalised by proposing a competition between a nonstereoselective electrophilic pathway of addition and a stereospecific pathway of oxygen insertion, the former being disfavoured by electron-withdrawing substituents. Alternatively, the formation of an open intermediate between the MnV oxene and the substrate could be suggested, where the stereoselectivity ought to be determined by the competition between closure of the epoxide ring and rotation around the C-C bond. In this case, the enhanced stereoselectivity given by our polyhalogenated porphyrins might be attributed to an acceleration of the epoxide ring closure caused by the electron-withdrawing effect of the halogen substituents.
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    The Effect of the Bite Angle of Diphosphane Ligands on Activity and Selectivity in Palladium-Catalyzed Cross-Coupling (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 155-157 
    Details
    ISSN: 1434-1948
    Keywords: Bite angle ; Catalysis ; P ligands ; Palladium ; Cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the natural bite angle (βn) of diphosphane ligands on catalyst selectivity and activity in the palladium-catalyzed cross-coupling of sec-butyl magnesium chloride with bromobenzene was investigated. The calculated natural bite angles range from 78° for dppe (1,2-bisdiphenylphosphanoethane) to 110° for Xantphos. The natural bite angle of diphosphane ligands has a large effect on catalyst selectivity and activity. Both rate and selectivity of the cross-coupling reaction increase with increasing bite angle and reach a maximum value with DPEphos (βn = 102.7° ). Larger bite angles of the diphosphane ligands result in a decreased selectivity and activity.
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    Oxidation of Polycyclic Aromatic Hydrocarbons Catalyzed by Iron Tetrasulfophthalocyanine FePcS: Inverse Isotope Effects and Oxygen Labeling Studies (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1269-1281 
    Details
    ISSN: 1434-1948
    Keywords: Oxidation ; Catalysis ; Phthalocyanine ; Iron ; Anthracene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iron(III) tetrasulfophthalocyanine (FePcS) was shown to catalyze the oxidation of polycyclic aromatic hydrocarbons by H2O2. Benzo[a]pyrene and anthracene were converted to the corresponding quinones while biphenyl-2,2′-dicarboxylic acid was the main product of phenanthrene oxidation. The mechanism of the anthracene oxidation by H2O2 in the presence of FePcS or by KHSO5 with iron(III) meso-tetrakis(3,5-disulfonatomesityl)porphyrin (FeTMPS) (see Figure 1 for catalyst structures) has been investigated in details by using kinetic isotope effects (KIEs) and 18O labeling studies. KIEs measured on the substrate consumption in the competitive oxidation of [H10]anthracene and [D10]anthracene by FePcS/H2O2 and FeTMPS/KHSO5 were essentially the same, 0.75 ± 0.02 and 0.76 ± 0.06, respectively. These inverse KIEs on the first oxidation step can be explained by the sp2-to-sp3 hybridization change during the addition of an electrophilic oxoiron complex to the sp2 carbon center of anthracene to form a σ adduct (this inverse KIE being enhanced by stronger stacking interactions between the perdeuterated substrate with the macrocyclic catalyst). Although the first oxidation step seems to be the same, different distribution of the oxidation products of anthracene and very different 18O incorporation into anthrone and anthraquinone in catalytic oxidations performed in the presence of H218O suggested that different active species should be responsible for anthracene oxidation in both catalytic systems. All the results obtained are compatible with an involvement of TMPSFeV=O (or TMPS+FeIV=O), having two redox equivalents above the iron(III) state of the metalloporphyrin precursor, while PcSFeIV=O (one redox equivalent above FeIII state of FePcS) was proposed to be the active species in the metallophthalocyanine-based system.
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    The Twofold Heck Reaction on 1,2-Dihalocycloalkenes and Subsequent 6π-Electrocyclization of the Resulting (E, Z, E)-1,3,5-Hexatrienes: A New Formal {2+2+2}-Assembly of Six-Membered Rings (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1521-1534 
    Details
    ISSN: 1434-193X
    Keywords: Heck reaction ; Cross coupling ; Palladium ; Catalysis ; 6π-Electrocyclization ; Cyclohexa-1,3-dienes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,6-Disubstituted (E, Z, E)-1,3,5-hexatrienes (4 and 5) were prepared by vicinal twofold Heck coupling reactions from 1,2-dibromocyclopentene (1), 1,2-dibromocyclohexene (2), 1,2-diiodocyclopentene (8), 1,2-diiodocyclohexene (9), 1-bromo-2-trifluoromethanesulfonyloxycyclohex-1-ene (11), or 1-chloro-2-nonafluorobutanesulfonyloxycyclohex-1-ene (19) with alkenes 3, e. g. methyl, tert-butyl, menthyl, 8-phenylmenthyl acrylate, styrene, and alkenylsilanes, respectively, in moderate to mostly good and very good yields (20-92 %). The coupling of alkenylsilanes 3f-k could only be achieved with the 1,2-diiodocycloalkenes 8 and 9, respectively. The corresponding hexatrienes 5 with two different substituents in the 1- and 6-positions were prepared by a sequence of two coupling reactions with different alkenes from 1-chloro-2-nonafluorobutanesulfonyloxycyclo-hex-1-ene (19) or by Wittig-Horner-Emmons olefination of 2-bromocyclohexene-1-carbaldehyde (24) and subsequent Heck reaction of the resulting (E,Z)-bromodienes 25. Several of the hexatrienes (4aa, ee, 5aa, ee, al, am, el) readily underwent a 6π-electrocyclization upon heating in an inert atmosphere to give the 5- or 6-ring-annelated cis-5,6-disubstituted cyclohexadienes 26, 27 (50-95 %). Starting from 5am 2,3-disubstituted tetrahydronaphthalene 28am was formed under oxidative conditions (air) in the reaction and in the work-up procedure. The bissilyl-substituted derivatives 4ff, jj, 5ff did not cyclize under thermal conditions, apparently due to the steric demand of the two silyl substituents which would have to end up cis with respect to each other in the cyclohexadiene products.
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    Clusters as Ligands - Large Assemblies of Transition Metal Clusters (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1835-1846 
    Details
    ISSN: 1434-1948
    Keywords: Clusters ; Catalysis ; Carboxylato complexes ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strategy of using functionalized clusters as ligands for cationic metal centers facilitates the construction of designed transition metal cluster assemblies. Examples of cluster metal carboxylates with conventional as well as novel structures are given and an application of these large molecular species to the generation of heterogeneous hydrogenation catalysts with unusual activities and selectivities is described.
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    [(Arene)(Diene)Fe] and [(Arene)(Diazadiene)Fe] Complexes: Preparation, Reactivity, and Catalytic Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 119-126 
    Details
    ISSN: 1434-1948
    Keywords: Arene complexes ; Catalysis ; Diazadiene complexes ; Iron ; Metal vapour ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two different routes to novel [(diene)(η6-2,6-dimethylpyridine)Fe] complexes are reported, both of which utilize metal vapour reactions. The presence of two small substituents on the 2,6-position of pyridine is essential for the η6-coordination of the heterocycle. Investigations on the reactivity and stability of the [(diene)(η6-arene)Fe] complexes are presented, including those of the benzene, phosphinine, and pyridine derivatives. These investigations give some hints to the relevant factors for determining the interaction between an iron atom and a π-coordinated neutral arene ligand, and their modification by a nitrogen or a phosphorus atom. Selective substitution of the 1,5-cyclooctadiene (COD) ligand of [(COD)(η6-arene)Fe] complexes by some 1,4-diaza-1,3-diene (DAD) derivatives is possible in the case of the benzene or phosphinine arene ligands, and [(DAD)(η6-arene)Fe] complexes are formed, but all DAD derivatives tested so far cause the complete disintegration of [(COD)(η6-2,6-dimethylpyridine)Fe]. [(DAD)(η6-arene)Fe] complexes exhibit a catalytic potential, which was evaluated by experiments on the catalytic cyclodimerization of 1,3-butadiene in the presence of [(Et2AlOEt)2] as a co-catalyst. This reaction yields up to 92% of 1,5-cyclooctadiene, and an almost quantitative butadiene conversion is possible in the presence of less than 0.1% of the catalyst. Structural investigations on [(N,N′-bis(cyclohexyl)ethylenediimine)(η6-toluene)Fe] 5a reveal some details of the Fe-DAD interaction. An effective electron back-donation from occupied iron d-orbitals into the π*-LUMO of the DAD is indicated.
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    Spectroscopic Evidence for Intramolecular MoVI(O2)····HO-C Hydrogen Bonding in Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 275-281 
    Details
    ISSN: 1434-1948
    Keywords: Molybdenum ; Peroxo complexes ; Hydrogen bonds ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring-opening reaction of epoxycyclohexane with 2-[3(5)-pyrazolyl]pyridine results in the formation of racemic trans-2-[3-(2-pyridyl)-1-pyrazolyl]cyclohexanol (1). Kinetic resolution with lipase B from candida antarctica gives the (1S,2S) enantiomer of 1, the solid-state structure of which was determined by X-ray crystallography, as an enantiomerically pure tridentate ligand. Investigation by NMR spectroscopy of the corresponding oxodiperoxomolybdenum complex 2, where 1 acts as a bidentate chelate, proves the formation of a weak intramolecular MoVI(O2)····HO-C bridge in CHCl3 solution. This H bonding is broken by solvents such as acetone, THF or DMF, which are capable of forming hydrogen bonds to alcohols. Intermolecular hydrogen bonds between the OH groups and molybdenum peroxo moieties are also found in the solid-state structure of 2, leading to a helical arrangement of the peroxo complexes.
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    New P,N-Chelate Ligands Based on Pyridyl-Substituted Phosphaferrocenes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1163-1168 
    Details
    ISSN: 1434-1948
    Keywords: Chelates ; P,N ligands ; Phosphaferrocene ; Catalysis ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new pyridyl-substituted phosphaferrocene ligands 3 and 6 are prepared by addition of lithiated pyridine or α-picoline to 2-formyl-3,4-dimethylphosphaferrocene (1). The ligands 3 and 6 react with [Cp*RuCl]4 in THF to give the P,N-chelate complexes [Cp*RuCl·3] (9) and [Cp*RuCl·6] (10) with high diastereoselectivity. Addition of monodentate ligands like CO or PPh3 to the complexes leads by displacement of the Ru-bound pyridyl group to the respective carbonyl or phosphane complexes with monodentate P-coordinated phospha-ferrocene ligands. Reaction of the ligand 6 with [(C3H5)PdCl]2 and NH4PF6 gives the seven-membered chelate complex [(C3H5)Pd·6]PF6 (13) which was characterized by X-ray diffraction. The ligands 3 and 6 were tested in the palladium-catalyzed asymmetric alkylation of 1,3-diphenylallyl acetate.
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    Selective Catalytic Oxidation of Alcohols by a Ruthenium-Copper Bifunctional System Using Molecular Oxygen (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1673-1675 
    Details
    ISSN: 1434-1948
    Keywords: Ruthenium ; Copper ; Oxidations ; Catalysis ; Alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of allylic and benzylic alcohols to aldehydes can be carried out at room temperature with molecular oxygen, in the presence of the bifunctional ruthenium-copper system (nPr4N)(RuO4)-CuCl acting as the catalyst.
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    Kinetics of the Enolisation Reactions of 3-Acetyl-2,5-dimethylfuran and of 2-Acetylselenophene (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1867-1872 
    Details
    ISSN: 1434-193X
    Keywords: Catalysis ; Metal ion catalysis ; Kinetics ; 3-Acetyl-2,5-dimethylfuran ; 2-Acetylselenophene ; Enolisation reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants for the enolisation reactions of title compounds have been measured by their rates of halogenation at 25 °C in water, in several buffers, in dilute hydrochloric acid, in dilute sodium hydroxide, and in the presence of some metal ion salts. The results have been compared with those previously obtained from the corresponding reactions of acetophenone and a number of other acetyl heterocycles. Electronegativity of the heteroatoms and the “π-excessive” nature of the heterocyclic rings appear to be the main factors determining the relative reactivities in the acid-catalysed reactions. Brønsted β values and isotope effects, kH/kD, point to a more symmetrical transition state for the investigated acetyl heterocycles than that for acetophenone in the general base-catalysed reaction. Metal-activating factors (MAF), i.e. the catalytic constant for metal-ion (Cu2+, Zn2+, and Ni2+) catalysis, kM, relative to that for proton catalysis, kH, are discussed as an empirical measure of the “hard or soft” character of the carbonyl groups in acyl heterocycles.
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    An Amidinate Ligand with a Pendant Amine Functionality; Synthesis of a Vanadium(III) Complex and Ethene Polymerization Catalysis[#] (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1867-1870 
    Details
    ISSN: 1434-1948
    Keywords: Vanadium ; Amidinate ; Ethene Polymerization ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new type of amidinate ancillary ligand has been prepared, which incorporates a pendant tertiary amine functionality. The crystal structure of a vanadium(III) derivative, [SiMe3NC(Ph)NCH2CH2NMe2]VCl2(THF) (1), shows that the ligand can adopt a facial geometry, with an unusual distortion of the amidinate nitrogen bearing the pendant functionality. With AlEt2Cl cocatalyst the compound 1 produces a single-site catalytic system for the polymerization of ethene.
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    Catalytic Formation of Oligopeptides from α-Amino Acid Esters with (p-Cymene)ruthenium(II) Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 729-731 
    Details
    ISSN: 1434-1948
    Keywords: Catalysis ; Oligomerization ; Organometallics ; Oligopeptides ; Ruthenium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Consecutive addition of one-equivalent portions of glycine ethyl ester to [(p-cymene)Ru(GGGOMe-H+)Cl] leads to considerable amounts of (tetra- to nonapeptide)ruthenium complexes in a one-pot reaction, in which the (p-cymene)RuCl fragment acts as a catalyst. The analogous reaction with alanine methyl ester affords AGGG and AAGGG complexes as the main products. The course of these metal-catalyzed peptide oligomerizations has been followed by mass spectrometry. The synthesis and characterization of the pentapeptide complex [(C6Me6)Ru(GGGGGOMe-H+)] is reported.
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    1,3-Asymmetric Induction in Stereoselective Rhodium-Catalyzed Hydroformylation of Homomethallylic Alcohols⋆ (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1123-1134 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Catalysis ; Hydroformylations ; Rhodium compounds ; Catalyst-directing groups ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Introducing ortho-diphenylphosphanyl benzoyl as a substrate bound catalyst directing group (CDG) allows an efficient substrate-directed diastereoselective hydroformylation of acyclic homomethallylic alcohols 5, making use of 1,3-asymmetric induction. The corresponding anti-aldehydes 10 were obtained as the major diastereomer in all cases, with diastereomer ratios of ca. 91:9 (anti:syn). Supporting evidence could be obtained for the ability of the o-DPPB group to act as a catalyst-directing group (CDG) via a reversible catalyst coordination. Finally, a model has been devised that rationalizes the origin of the 1,3-asymmetric induction. This model is based on a conformational analysis (NMR studies, MACROMODEL/MM3 calculations) of the homomethallylic substrates and indicates a relationship between the preferred substrate conformation and the experimentally determined stereoselectivities. In agreement with this model was the predicted significant improvement in stereoselectivity upon hydroformylation of the anti-homomethallylic alcohol derivative 15 (→ 21).
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    Nazarov Cyclization of Bis([2.2]paracyclophane-1,9-dienyl) Ketone: First Synthesis of a Bis([2.2]paracyclophane)-Annelated Cyclopenta-1,4-diene (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2301-2304 
    Details
    ISSN: 1434-193X
    Keywords: Five-membered rings, formation of ; Electrocyclic reactions ; Cyclopentane derivatives, sterically crowded ; Lewis acids ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The annelation of five-membered rings onto the bridges of [2.2]paracyclophane-1,9-diene (1) can be achieved via Nazarov cyclization. Depending on the reaction conditions, bis([2.2]paracyclophane-1,9-dienyl) ketone (4) yielded the cy-clopentenone 8 or the α-substituted cyclopentanones 3-7 with two annelated [2.2]paracyclophane units. The synthesis of 1:2-(1:2-[2.2]paracyclophane-1,9-dieno)-4:5-(9:10-[2.2]paracyclophane-1-eno)cyclopenta-1,4-diene (10) from 8 as a potential ligand for metallocene complexes and generation of its anion 11 is also described.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1998/98200_s.pdf or from the author.
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    Chromium Complex Catalyzed Synthesis of Spirocyclopropanes from Diaryl Diazo Compounds - Direct NMR-Spectroscopic Observation of a Carbene Complex Intermediate (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1011-1022 
    Details
    ISSN: 1434-193X
    Keywords: Cyclopropanation ; Chromium ; Catalysis ; Carbene complex ; Diazo compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [2 + 1] cycloaddition reaction of electron-rich alkenes such as enol ethers with 9-diazo-9H-fluorene (1) is efficiently catalyzed by pentacarbonyl(η2-cis-cyclooctene)chromium(0) (2). This cyclopropanation reaction shows a pronounced preference for electron-rich C=C bonds, as demonstrated by the regioselective reactions of allyl vinyl ether and 2-vinyloxyethyl acrylate; the [2 + 1] cycloaddition proceeds via the carbene complex intermediate 13, which has been detected by 13C-NMR spectroscopy in the course of the reaction. (Z)-Propenyl benzyl ether yields spirocyclopropane 21 with retention of the configuration of the former olefinic double bond. Whereas diazo compounds 22 and 23 react with ethyl vinyl ether to give low yields of cyclopropanes, the dibenzocycloheptenylidene and diarylcarbene precursors 24 and 25 afford moderate yields of olefin metathesis products 29-31. The competition between cyclopropanation and olefin metathesis reflects the propensity of the carbene complex intermediates to undergo decarbonylation.
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    Transition-Metal Catalysis of the Michael Reaction of 1,3-Dicarbonyl Compounds and Acceptor-Activated Alkenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1259-1266 
    Details
    ISSN: 1434-193X
    Keywords: Catalysis ; Carbonyl compounds ; Lanthanides ; Michael reaction ; Transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition-metal catalysis of the Michael reaction of 1,3-dicarbonyl compounds with acceptor-activated alkenes is introduced as a valuable alternative to the classic base catalysis of this reaction. Owing to the mild, neutral reaction conditions, the chemoselectivity of these processes is superior to that offered by the base catalysis, since the latter suffers from various unwanted side- and subsequent reactions, such as aldol cyclizations and ester solvolyses. The most efficient transition-metal catalysts do not require inert or anhydrous conditions, even solvents are unnecessary in some cases, and quantitative conversions can be achieved at room temperature. Furthermore, the development of transition-metal catalysts on solid supports has allowed very simple work-up procedures. Despite the extraordinary chemoselectivity, in terms of diastereoselectivity transition-metal catalysis gives better results than base catalysis only in a very few special cases. Also, in terms of enantioselectivity, results recently achieved with basic rare-earth metal catalysts cannot be reproduced by transition metals. Nevertheless, with transition-metal catalysis, even new reactivities can be observed, which have hitherto been unknown for base-catalyzed systems. For example, Michael donor molecules have been found to react in an unprecedented vinylogous fashion.
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    Concave Pyridines for Selective Acylations of Polyols (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1077-1084 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Catalysis ; General base ; Macrocycles ; Molecular recognition ; Hydrogen bond ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selectivity enhancements in the base-catalyzed acylation of polyols (1,2- or 1,3-alkanediol, partially protected glucoside) have been found with (bi)macrocyclic pyridines 2 and 9 as catalysts. The different selectivities obtained for concave pyridines of varying ring sizes (1 vs. 2) are probably caused by their different geometries as a number of X-ray analyses (1a, 1b, 2a, 2b, 2e, 9) indicate. The methyl glucoside 7 can selectively be acylated in 2-position.
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    A Vinylogous Donor in an Iron(III)-Catalysed Michael Reaction and an Enone-Dienol Tautomerism (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 759-761 
    Details
    ISSN: 1434-193X
    Keywords: Catalysis ; Carbonyl compounds ; Iron compounds ; Michael reactions ; Tautomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A double acceptor-activated cycloalkene 1 reacts in an FeCl3 · 6 H2O catalysed Michael reaction surprisingly as a donor. The constitution of the product 2 results from a reaction of 1 in the γ-position, thus the Michael reaction is vinylogous with respect to the donor. A tautomerism between the enone 1 and the dienol 4 is found to be a precondition for this reactivity.
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    The Effect of the Bite Angle of Diphosphane Ligands on Activity and Selectivity in Palladium-Catalyzed Allylic Alkylation (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 25-27 
    Details
    ISSN: 1434-1948
    Keywords: Bite angle ; Catalysis ; P ligands ; Palladium ; Allylic alkylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the natural bite angle (βn) of diphosphane ligands on catalyst selectivity and activity in the palladium-catalyzed allylic alkylation was investigated. The selectivity and rate of the reaction are mainly determined by steric hindrance induced by the diphosphane ligands. The steric hindrance at the palladium center increases as the natural bite angle of the ligand becomes larger. This results in an increasing selectivity at larger bite angles, but at very large bite angles the rate of the reaction drops. The ligand with the largest calculated bite angle, Xantphos, induced 100% selectivity but the reaction rate became low.
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    Phosphapalladacycle-Catalyzed Heck Reactions for Efficient Synthesis of Trisubstituted Olefins: Evidence for Palladium(0) Intermediates (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 29-35 
    Details
    ISSN: 1434-1948
    Keywords: Catalysis ; Palladium ; C-C coupling ; Metallacycles ; Trisubstituted olefins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coupling reaction of 1,1-disubstituted olefins (α-methylstyrene, n-butyl methacrylate) with various aryl bromides (Heck reaction) has been studied as a new concept to synthesize trisubstituted olefins. Surprisingly, the nature of the base dramatically influences the product distribution. Thus, a systematic investigation on the role of base in Heck reactions of 1,1-disubstituted olefins was performed. Less coordinating bases like NaOAc, NaOBz or Na2CO3 yield a statistical distribution of regioisomers with the terminal olefin 10 as the major product. However, by using amines like Bu3N or diisopropylethylamine (DIPEA) as base internal olefins can be synthesized with high selectivities. With phosphapalladacycle 3 as catalyst precursor, we were able to obtain catalyst turnover numbers up to 1000, while Pd(OAc)2/2PPh3 was one order of magnitude less active. Analysis of the reaction profile by kinetic investigations led to the postulation of a reduction and subsequent oxidative addition of the catalyst precursor 3 to form 12 as catalytically active intermediate.
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    Polymerization of propylene by mixed Ziegler-Natta and metallocene catalysts (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 401-408 
    Details
    ISSN: 0268-2605
    Keywords: Metallocene ; Ziegler-Natta ; Polypropylene ; α-Olefins ; Catalysis ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization of propylene using a mixture of racemic metallocenes and Ziegler-Natta catalysts was investigated. The polypropylene was obtained as a mixture of a fine powder and beads, with the powder being absorbed partially on the beads. The relative amount of the powder can be controlled by the concentration of the metallocene. The compatibility between the components of the mixed catalytic systems and the effect of the components on the rate of polymerization and on the properties of the new polymers were studied. The metallocene system dramatically affects the melt viscosity, isotacticity and molecular weight of the polymers. The two catalytic systems are able to act jointly, producing different polymers, for which separate melting and crystallization temperatures are obtained. © 1998 John Wiley & Sons, Ltd.
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    Synthesis of Functionalized Carbamates through a Palladium-Catalyzed Reductive Carbonylation of Substituted Nitrobenzenes (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 13-22 
    Details
    ISSN: 0009-2940
    Keywords: Carbamates ; Catalysis ; Substituted nitrobenzenes ; Palladium ; Reductive carbonylation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The palladium-catalyzed reductive carbonylation of ortho and para-substituted nitrobenzenes has proven to be an attractive route for the synthesis of functionalized carbamates. For the Pd(1, 10-phenanthroline)2(triflate)2 catalyst system, the scope of the reaction has been studied. Substrates with electron-donating substituents at the para position were found to decrease the catalytic activity, most probably as a result of their relatively low oxidizing capacity. the selectivity towards the desired carbamate, however, was increased for these substrates. Under the influence of electron-withdrawing substituents the azoxybenzene and azobenzene derivatives became important side products. Introduction of large steric hindrance at the ortho position of the nitro substrates gave rise to an interesting side reaction, viz. methoxylation of the aromatic ring. The methoxylation reaction appeared to occur on an intermediate species in the catalytic cycle. Several functionalities have shown to be resistant to the reaction conditions required for the conversion ot the nitro group. Especially with 4-nitrobenzoic acid, an extremely high activity and selectivity was found, thus yielding a very convenient synthesis for N-protected amines containing carboxylic acid function.
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    URL: http://dx.doi.org/10.1002/cber.19971300104
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    A Specific Route to Enantiomerically Pure Asymmetric (η6-Arene)(η4-1,5-cyclooctadiene)Ru(0) ComplexesDedicated to Professor Rolf Gleiter on the occassion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 123-130 
    Details
    ISSN: 0009-2940
    Keywords: Arene complexes ; Ruthenium compounds ; Electrophilic substitution ; Lithiation ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral or achiral (arene)(COD)Ru complexes can be made by replacing the η6-ligands of (η4-1,5-COD)(η6-1,3,5-cyclooctatriene)Ru (1) or (η4-1,5-COD)(η6-naphthalene)Ru (2) by a suitable arene. This well known reaction has been extended to mono- and dibromoarenes and we report a novel route to substituted (arene)(COD)Ru species, utilizing (bromoarene)-(COD)Ru as starting materials. These facilitate a rapid bromine-lithium exchange reaction with nBuLi at low temperatures and the lithiated species react readily with alkyl chloroformates as electrophiles. By using chiral electrophiles [alkyl = (-)-menthyl] enantiomerically pure or diastereomeric complexes containing CO2R* groups are formed, depending on the symmetry of the original complex. A diastereomeric 1:1 mixture was separated by recrystallization. All (arene)-(COD)Ru complexes tested so far are useful as catalysts for the hydrogenation of simple alkenes at room temperature.
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    URL: http://dx.doi.org/10.1002/cber.19971300121
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    New Coupling Reactions and Phosphorylations Using Organozinc Reagents (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1021-1027 
    Details
    ISSN: 0009-2940
    Keywords: Zinc ; Chirality ; Cross-coupling ; Phosphorylations ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This Microreview on the chemistry of organozinc reagents starts by briefly showing the methods of preparation of organozinc compounds and then discusses the considerable synthetic utility of zinc organometallics for the formation of new carbon-carbon bonds in the presence of transition-metal catalysts. Finally, the use of organozinc chemistry for the preparation of polyfunctional and chiral phosphanes is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300802
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    Molybdenum-Catalysed and -Mediated Cycloaddition Reactions: Efficient Synthesis of Complex Products from 1-Oxa-1,3-dienes and Cyclotrienes or -tetraenes (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 453-462 
    Details
    ISSN: 0009-2940
    Keywords: Cycloadditions ; Catalysis ; 1-Oxa-1,3-dienes ; Molybdenum ; stereoselectivity ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molybdenum-mediated [6 + 2]-cycloaddition reactions of unsaturated ketones to cyclotri- or -tetraenes, e.g. cyclohepta-1,3,5-triene or cyclooctatetraene, proceed under very mild conditions, in high yields and with excellent stereoselectivity starting from the appropriate dicarbonylbis[π4-(1-oxa-1,3-diene)]molybdenum complexes. The stereochemistry of the product arising from the reaction of dicarbonylbis[π4-(5-methylhex-3-en-2-one)]molybdenum with cyclohepta-1,3,5-triene allows one to deduce a stepwise mechanism for this addition. The reactants are fused, as would be expected from an exo-type approach, thus indicating an intermolecular attack of the cycloheptatriene. Tungsten oxadiene complexes are effective in analogous reactions at somewhat reduced reaction rates. Catalytic cycloadditions are observed in several cases when 1-5 mol% of the highly reactive dicarbonylbis[π4-(R-(+)-pinocarvone)]molybdenum is employed as the catalyst. Cycloadducts are formed diastereospecifically in most cases. When cyclooctatrienes are employed as reactants, a sequence of electrocyclization of the triene and subsequent [4 + 2]-cycloadditon occurs with high selectivity and efficiency, leading to a pentacyclic ketone. The product structure reveals an endo-type approach of the polyene in this case.
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    URL: http://dx.doi.org/10.1002/cber.19971300404
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    Contributions of the Chemistry of Boron, 236. In Quest of New and Stable Bis(organyloxy)boranes (RO)2BH for Catalytic HydroborationDedicated to Prof. Dr. Marianne Baudler on the occasion of her 75th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 363-370 
    Details
    ISSN: 0009-2940
    Keywords: Bis(triphenylmethoxy)hydroborane ; Naphtho[2,3-d], -1,3,2-dioxaborolane ; Naphtho[1,8-de]-1,3,2-dioxaborinane ; Phenanthro[9,10-d]-1,3,2-dioxaborolane ; Dibenzol[d,g]-1,3,2-dioxaborocine ; Bis(diphenylmethoxy)borane ; Tetrachlorobenzo-1,3,2-dioxaboraolen ; Hydroborations ; Boron ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New and stable bis(organyloxy)boranes, 1,3,2-dioxaborolanes and 1,3,2-dixoaborinanes have been prepared (i) from the corresponding diol and BH3·THF and (ii) from 1,2-diketones and BH3·THF. They were characterized by spectroscopic techniques. The BH stretching frequency seems to be a measure of ring strain and Lewis acidity. The compounds have been qualitatively tested in the transition-metal-catalysed hydroboration of cyclopentene, and the dioxaborinane 11 proved to be superior to the 1,3,2-dioxaborolanes 9 and 18.
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    Chlorides and Acetylacetonates of Transition Metals as Catalysts for the Oxidation of 1-Indanol by Sodium Percarbonate (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1655-1658 
    Details
    ISSN: 0009-2940
    Keywords: Catalysis ; Oxidations ; Transition metals ; Sodium percarbonate ; 1, 2-Dichloroethane ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The screening of metal chlorides and metal acetylacetonates as catalysts for the oxidation of 1-indanol by sodium percarbonate (at reflux in 1,2-dichloroethane in the presence of small amounts of Adogen 464) has been carried out. The efficiency of the process depended on the nature of the transition metal and its oxidation state but, except for iron, was not greatly influenced by the nature of the ligands. Good conversions and yields have been obtained using PdCl2, RhCl3, RuCl3 and, particularly, MoO2(acac)2 as catalysts.
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    Cobalt-Catalyzed Selective Oxidation of the Tritertiary Phosphane Triphos with Molecular OxygenDedicated to Professor H. Bärnighausen on the occasion of his 65th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1393-1403 
    Details
    ISSN: 0009-2940
    Keywords: Tripod ligands ; Phosphane oxides ; Cobalt ; Oxidation ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactivity of complexes of triphos [CH3C(CH2PPh2)3] and CoCl2 towards dioxygen has been investigated. Reaction of the pseudo-tetrahedral complex (η2-triphos)CoCl2 (1) with dioxygen yields after work-up the mixed phosphane/phosphane oxide ligands triphosO and triphosO2. The novel ligand triphosO2 can be obtained in quantitative yield using catalytic amounts of 1. In order to gain some insight into the catalytic dioxygen activation reaction, experiments with various triphos/Co/Cl species, in different solvents and at several concentrations have been carried out. A mechanism involving two separate reaction pathways is proposed. Complexes of triphosO and triphosO2 with CoCl2, [η2-(P, P)-triphosO]CoCl2 (4), and [η2-(P, O)-triphosO2]CoCl2 (5), which are present as intermediates in the oxygenation reaction, have been isolated and fully characterized including X-ray structural analyses.
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    URL: http://dx.doi.org/10.1002/cber.19971301007
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    Chemical Interconversions in the System TP*Zn/CO2/Alcohol [Tp* = Substituted Tris(pyrazolyl)borate]Dedicated to Prof. Walter Siebert on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 101-104 
    Details
    ISSN: 0009-2940
    Keywords: Zinc complexes ; Alkyl carbonate complexes ; CO2 fixation, reversible ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The zinc hydroxide complexes Tp*Zn-OH with TpCum,Me = tris(3-cumenyl-5-methylpyrazolyl)borate and TptBu,Me = tris(3-tert-butyl-5-methylpyrazolyl)borate can be converted to the alkyl carbonate complexes Tp*Zn-OCOOR by reaction with dialkyl dicarbonates or with alcohol and CO2. An alternative formation reaction is the treatment of the pyrazolyl borate with zinc perchlorate and potassium carbonate in alcohol. The interconversion between TpCum,MeZn-OH and TpCum,MeZn-OCOOMe in methanol-containing solution can be repeatedly performed in both directions by bubbling either CO2 or N2 through the solution. The alkyl carbonate complexes show a variable sensitivity towards hydrolytic destruction with reformation of the hydroxide complexes. The complexes TptBu,MeZn-OCOOR (R = Me, Et) release CO2 under high vacuum to form the alkoxide complexes TptBu,Me-Zn-OR, which could not be obtained pure due to their extreme water sensitivity. Indirect evidence for their existence is also obtained by the reaction between TpCum,MeZn-OCOOMe and methyl iodide, forming TpCum,MeZn-I and dimethyl ether. The Zinc hydroxide complexes catalyse the formation of diethyl carbonate from ethanol and CO2.
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    Switch from Palladium-Catalyzed Cycloisomerization/Dimerization of Terminal Allenyl Ketones to Preferential Formation of Monomers by a 5-Palladatricyclo[4.1.0.02,4]heptane Catalyst: Synthesis of Furans from Substrates Incompatible with the Commonly Used Silver Catalysts (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1449-1456 
    Details
    ISSN: 0009-2940
    Keywords: Alkynes ; Allenes ; Furans ; Palladium ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By making the choice of either PDCl2(MeCN)2 or PTH rac-4 as catalyst, the allenyl ketones 1 could be preferentially cycloisomerized/dimerized to either 2,4-disubstituted furans 3 or preferentially cycloisomerized to the monosubstituted furans 2. Since the PTH catalyst tolerates functional groups like terminal alkynes, α-halogen ketones, and alkyl halides that inhibit the silver catalysis, the latter method is an important extension of Marshall's Ag1-catalyzed isomerization of 1 to 2. Some of these latter reactions also showed exciting chemoselectivities, e.g. with allenyl ketones, such as 1c and 1d, which also also possess a 1,6-enyne substructure, no enynecyclization was observed. This is also the first reported example of catalysis by a PTH.
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    URL: http://dx.doi.org/10.1002/cber.19971301015
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    The Kinetics of the Catalyzed CVD of Monocrystalline α-Silicon Nitride FilamentsFinancial support of these studies by the German Research Foundation (DFG) is gratefully acknowledged. Also, the assistance of Priv.-Doz. P. Uggowitzer, ETH Zürich, in calculating nitrogen solubility data for various iron alloys is gratefully acknowledged. (1997)
    Weinheim : Wiley-Blackwell
    Chemical Vapor Deposition 3 (1997), S. 51-58 
    Details
    ISSN: 0948-1907
    Keywords: Silicon nitride filaments ; CVD ; Catalysis ; Kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Catalyzed chemical vapor deposition of α-silicon nitride filaments from silicon subhydrides and ammonia was studied using calculation of nitrogen solubility in selected catalysts (silicon-containing iron alloys), both in the solid and liquid-state, by filament deposition experiments with catalysts of various composition and size, and by variation of the flow rates and partial pressures of precursor gases, the silicon subhydrides and ammonia. The results show that neither nitrogen solubility in, nor nitrogen diffusion through the catalyst plays a determining role in the deposition kinetics, as has been previously suggested. Instead, the deposition rate is determined by the partial dissociation of ammonia, which can be accelerated by adding diluent gases with a sufficiently high collision cross section. The catalyst material has an additional, strongly accelerating effect. The present state of research suggests that nitrogen is the preferred diluent gas and chromium an optimum alloying element.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/cvde.19970030108
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    Combinatorial Libraries: Studies in Molecular Recognition and the Quest for New Catalysts (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 637-647 
    Details
    ISSN: 0947-3440
    Keywords: Combinational libraries ; Molecular recognition ; Receptors ; Ligands ; Catalysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Combinatorial libraries offer a new powerful tool for gathering empirical information about host/guest interactions and for developing catalysts for organic reactions. Combinatorial approaches to molecular recognition are discussed, i.e. screening of libraries of ligands with synthetic receptors and libraries of synthetic receptors with the ligands for which selective binding is desired. Recent achievements in the development of new catalysts for organic synthesis using combinatorial approaches are also reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970405
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    Synthese, Struktur und Oxotransferreaktionen von Dioxomolybdän(VI)-Komplexen mit mehrzähnigen Aminoalkoholen als Liganden (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 997-1005 
    Details
    ISSN: 0044-2313
    Keywords: Amine Alcohol Ligands ; Catalysis ; DMSO Reductases ; Molybdenum Complexes ; Oxygen Atom Transfer ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis, Structure, and Oxygen Atom Transfer Reactions for Dioxomolybdenum(VI) Complexes with Multidentate Amine AlcoholsThe trivalent, pentadentate amine alcohol ligands l,l-bis(2-hydroxyethyl)-4-(2-hydroxybenzyl)-l,4-diazabutane (H3hebab) and N-salicylidene-2-(bis(2-hydroxyethyl)amino)-ethylamine (H3sabhea) react with [MoO2(acac)2] in methanol solution to yield the cis-dioxomolybdenum(Vl) complexes [MoO2(Hsabhea)] (1) und (MoO2(Hhcbab) (2). The complexes have been characterized by 1H and 13C NMR, vibrational (IR, Raman), and UV/Vis spectroscopy as well as crystal structure analyses (1: monoclinic space group P21/c, a = 1583.6(5), b = 681.2(3), c = 1332.8(5) pm, β = 101.42(3)°, Z = 4; 2: monoclinic space group P21/c, a = 2096.5(4), b = 755.5(1), c = 2000.4(4) pm, β = 112.26(1)°, Z = 8), For both complexes the molybdenum center possesses a distorted octahedral environment with the oxo ligands oriented trans to the nitrogen donor centers of the respective ligand system. In the case of 1 this leads to a sterically strained facial coordination of the imine-chelate fragment established by the phenolate oxygen and imine as well as tertiary amine nitrogen donors. This is in contrast to the usually prefered meridional coordination of such an imine-chelate fragment. The catalytic activity of the complexes 1 and 2 toward oxygen atom transfer is investigated for the model reaction between DMSO and triphenylphos-phane. Both complexes catalyse the oxidation of triphenylphos-phane by DMSO, with the marked contrast that 1 is the much more efficient catalyst. This observations can be explained on the bases of the structural differences between the complexes 1 and 2.
    Notes: Die dreibasigen, fünfzähnigen Aminoalkohole l,l-Bis(2-hydroxyethyl)-4-(2-hydroxybenzyl)4,4-diaza-butan (H3hebab) und N-Salicyliden-2-(bis(2-hydroxyethyl)-amino)ethylamin (H3sabhea) reagieren mit [MoO2(acac)2] in Methanol als Lösungsmittel zu den cis-Dioxomolybdän(VI)-Komplexen [MoO2(Hsabhea)] (1) und [MoO2(Hhebab)] (2). Die Komplexe wurden mit Hilfe von 1H-NMR-, 13C-NMR-, Schwingungs- (IR, Raman) und UV/Vis-Spektroskopie sowie Kristallstrukturanalysen (1): monokline Raumgruppe P21/c; a = 1583,6(5); b = 681,2(3); c = 1332,8(5) pm; β = 101,42(3)°; Z = 4; 2: monokline Raumgruppe P21/c; a = 2096,5(4); b = 755,5(1); c = 2000,4(4) pm; β = 112.26(1)°; Z = 8) charakterisiert. In beiden Komplexen besitzt das Molybdän(VI)-Zentrum eine verzerrt oktaedrische Umgebung, dabei sind die Oxo-Liganden jeweils trans-ständig zu den beiden Stickstoffdonorzentren der Ligandgerüste. Für 1 führt dies zu einer sterisch gespannten facialen Koordination der üblicherweise meridional koordinierten Imino-Chelateinhcit des Ligandgerüsts, bestehend aus Phenolatsauerstoff- bzw. Imin- und tertiärem Aminstickstoffdonor. Die Reaktivität der Komplexe 1 und 2 bezüglich der Sauerstoffübertragung wird am Beispiel der Modellreaktion zwischen DMSO und Triphenylphosphan untersucht. Beide Komplexe katalysieren diese Reaktion, wobei 1 jedoch deutlich reaktiver ist. Die beobachtete Reaktivitätsabstufung läßt sich im wesentlichen auf die strukturellen Unterschiede der Komplexe 1 und 2 zurückführen.
    Additional Material: 5 Ill.
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    Metal-Catalyzed Oxidations, 4Part 3: Ref.[1].. The Reaction of Molybdenumperoxo Complexes with Brønsted and Lewis Acids (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 575-580 
    Details
    ISSN: 0009-2940
    Keywords: Molybdenum complexes ; Peroxo complexes ; Catalysis ; Olefin epoxidation ; Proton transfer ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NMR studies of the reaction of complexes of the type (L-L)MoO(O2)2 (L - L= bidentate ligand) with strong Brønsted and Lewis acids prove that protons are transferred preferentially to an η2-peroxo and not to the oxo ligand. This behavior in proton transfer reactions is one critical point of the catalytic activity of such complexes in olefin epoxidation. EH calculations on the model complex (NH3)2MoO(O2)2 support the spectroscopic investigations.
    Additional Material: 7 Ill.
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    Palladium-Copper-Catalyzed Coupling of Tricarbonylchromium-Complexed Phenylacetylene with Iodoarenes - A Facile Access to Alkynyl-Bridged Cr(CO)3-Complexed Benzenes (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 607-613 
    Details
    ISSN: 0009-2940
    Keywords: Arene complexes ; Chromium compounds ; Alkynes ; Catalysis ; Coupling reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The palladium-copper-catalyzed coupling of the tricarbonyl-chromium-complexed chlorobenzene 1 with (trimethylsilyl)-acetylene gives tricarbonyl{η6-[(trimethylsilyl)ethynyl]-benzene}chromium(0) (2) in high yield. After desilylation of 2 tricarbonyl[η6-(ethynylbenzene)]chromium(0) (3) is obtained quantitatively. Using the palladium-copper-catalyzed methodology, we can readily introduce Cr(CO)3-complexed phenylethynyl units by a multifold coupling of 3 with iodobenzene, 1,2-, 1,3-, 1,4-di- and 1,3,5-tiiodobenzene (4a-e) or 1 to give polynuclear Cr(CO)3-complexed (phenylethynyl)benzenes 5a-e and doubly Cr(CO)3-complexed tolane 6 in good to moderate yield. The crystal structure analyses of μ3-{η6:η6:η6[1,3,5-benzenetriyltris(2,1-ethynediyl)]tris(benzene)}tris[tricarbonylchromium(0)] (5e) and μ-{η6:η6-[1,2-ethynediylbis(benzene)]}bis[tricarbonylchromium(0)] (6) reveal that the tricarbonylchromium tripods in the same molecule are arranged in antiparallel syn-eclipsed conformations. The Eglington coupling of 3 affords a doubly Cr(CO)3-complexed diphenylbutadiyne 7 in excellent yield.
    Additional Material: 2 Ill.
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    Activation of Bis(trimethylsilyl) Peroxide and tert-Butyl Hydroperoxide with Oxo and Peroxo Complexes of Vanadium, Molybdenum, and Tungsten for the Sulfoxidation of Thianthrene 5-Oxide (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 1177-1182 
    Details
    ISSN: 0009-2940
    Keywords: Thianthrene 5-oxide ; Peroxide, bis(trimethylsilyl) ; Hydroperoxide, tert-butyl ; Oxygen transfer ; Peroxo complexes ; Catalysis ; Vanadium ; Molybdenum ; Tungsten ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(trimethylsilyl) peroxide (BTSP) and tert-butyl hydroperoxide (tBuOOH) were activated by various oxo and peroxo complexes of molybdenum, tungsten, and vanadium as catalysts for the sulfoxidation of thianthrene 5-oxide (SSO). A screening of a number of phosphane oxide and amine oxide ligands revealed that BTSP was most efficiently activated by the [MoO5(OPtBu3)] complex. The best results for tBuOOH as oxygen source were achieved with the vanadates [VO(OR)3] (R = tBu, iPr). Comparative selectivity and rate data for the stoichiometric and catalytic sulfoxidations of SSO mediated by the MoO5L complex (L = OPtBu3, OPnOct3, ONnBu3, ONnOct3) suggest that the bisperoxo metal complex is the active oxygen transfer species.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19961291006
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    A Palladium-Catalyzed Domino Coupling Process Leading to Annelated PentafulvenesDedicated to Professor Dr. Peter Sartori on the occasion of his 65th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 1265-1269 
    Details
    ISSN: 0009-2940
    Keywords: Domino coupling reactions ; Pentafulvenes ; Catalysis ; Palladacycles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Annelated pentafulvenes 2, 10, 13, and 14 are efficiently accessible by a palladium-catalyzed domino coupling process of aryl substituted vinylic bromides 1, 9, 11, and 12, 5-Membered palladacycles 3 are discussed as key intermediates.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19961291019
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    The Catalytic Ring-opening Cyclooligomerization (ROC) of Thietane by the Complexes M(CO)5L (M = Cr and W; L = CO, thietane and 1,5,9-Trithiacyclododecane) (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 313-318 
    Details
    ISSN: 0009-2940
    Keywords: Thietane ; Catalysis ; Tungsten ; Macrocycle ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following four compounds have been synthesized: M(CO)5L (3 and 4, where M = Cr and W, and L = H2), W(CO)5(12S3) (5, where 12S3 = 1,5,9-trithia-cyclododecane), and [W(CO)5]2(12S3) (6). The molecular structures of 4 and 5 were established by single-crystal X-ray diffraction analyses. Both compounds contain a W(CO)5 group coordinated to one of the sulfur atoms of the hetero-cycle. The ability of the compounds M(CO)6, 1 and 2 (M = Cr and W), and 3 - 5 to catalytically produce ring opening cyclooligomerization (ROC) of thietane into 12S3 and 24S6, (24S6 = 1,5,9,13,17,21-hexathiacyclotetracosane) has been investigated. Compounds 1 - 3 have relatively low activity. Compounds 4 and 5 have the highest activity and selectivity for 12S3 formation. Crystal Data for 4: space group = P212121, a = 12.906(2) Å, b = 13.730(4) Å, c = 6.427(1) Å, Z = 4, 1306 reflections, R = 0.033; for 5: space group = P1¯, a = 12.703(1) Å, b = 13.510(2) Å, c = 5.833(1) Å, α = 101.75(1)°, β = 97.54(1)°, γ = 101.70(1)°, Z = 2, 2225 reflections, R = 0.023.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19961290311
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    Palladium-Catalyzed Reactions in Industry, 4[Part 3: Ref.[1].]. Synthesis of New Palladium Catalysts: First Isolation and Characterization of all Intermediates in a Cyclopalladation Reaction (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 1259-1264 
    Details
    ISSN: 0009-2940
    Keywords: Palladium ; Phosphanes ; Catalysis ; Cyclopalladation reaction ; Metallacycles ; CH activation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to synthesize chiral palladacycles for stereoselective C-C coupling reactions we studied the cyclopalladation of P-chiral phosphanes 2 and 3. New palladium complexes of the type L2PdX2 (6, 8) and LXPd-μ-X2-PdXL (5, 9, X = Cl; L = 2, 3) were isolated. A detailed study of the reactivity of all intermediates towards cyclopalladation proved the mechanism of cyclometalation reactions of o-tolylphosphanes for the first time. Different deuteration experiments clearly demonstrated the higher reactivity of dimeric palladium complexes towards metalation compared to monomeric species. In agreement with this observation only 5 and 9 gave the cyclopalladated products 4 and 10 as revealed by FAB mass spectrometric investigations. Under the described reaction conditions the synthesis of the corresponding palladacycles 4, 10 is not possible because cyclometalation is a reversible process with LXPd-μ-X2-PdXL as thermodynamic more stable products. The results demonstrate the importance of free coordination sites on the metal atom for cyclometalation reactions or more general CH activation processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961291018
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    Supramolecular Chemistry, 62Part 61: M. Fernandez-Saiz, H.-J. Schneider, J. Sartorius, W. D. Wilson, J. Am. Chem. Soc. 1996, accepted.. Ligand and Cosubstrate Effects on the Hydrolysis of Phosphate Esters and DNA with LanthanoidsDedicated to Prof. Dr. Dr. h.c. Michael Hanack on the occasion of his 65th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1757-1767 
    Details
    ISSN: 0947-3440
    Keywords: Phosphate esters ; DNA ; Hydrolysis ; Catalysis ; Lanthanoid cosubstrates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Attempts are described to enhance the catalytic activity of lanthanide ions by providing cosubstrates with an increasing number of nucleophilic groups or by attaching corresponding polyols covalently to stronger metal-binding centers like diazacrown ethers. Although the kinetic effects on the hydrolysis of bis(4-nitrophenyl) phosphate (BNPP) and of super-coiled plasmid DNA are only moderate, their dependence on cosubstrate structure and polyol configuration unambiguously demonstrates that these are involved in the slow step of the reactions. Thus, addition of gluconic acid to a LaCl3 solution leads to a marked increase of DNA cleavage from 20 to 71%. Naphthyl units covalently bound to the diazacrown show little effect on BNPP hydrolysis, but enhance DNA hydrolysis again from e.g. 38% (RF II) to 60%. Preliminary affinity measurements with calf thymus DNA, using a fluorimetric assay with ethidium bromide, show for polyamines a dependence on the number of ligand charges as observed earlier. The naphthyl compound is characterized by a high affinity; preliminary NMR data indicate that the naphthyl units intercalate into DNA.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/jlac.199619961109
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    Bifunctional Catalysis of Ester Aminolysis - A Computational and Experimental Study (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1501-1509 
    Details
    ISSN: 0947-3440
    Keywords: Aminolysis ; Esters ; Pyridones ; Catalysis ; Calculations, ab initio ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various pathways for the reaction of methylamine with methyl acetate catalyzed by 2(1H)-pyridone have been investigated at the Becke3LYP/6-31G**/HF/6-31G** level of theory. The most favorable pathway consists of a one-step reaction, in which all bond-forming and -breaking processes occur in concert. These modeling studies also show the pyridone to function as an acid, which led to the investigation of several substituted pyridones. 4-Cyano-, 3-cyano-6-methyl-, and 3-cyano-2(1H)-pyridone have indeed been shown to provide better catalysis in the ester aminolysis reaction by ab initio modeling at the Becke3LYP/6-31G**/HF/3-21G level. In order to verify the theoretical results, the catalytic activities of various substituted 2-pyridones in the reaction of n-butylamine with p-nitrophenyl acetate in chlorobenzene solution have been determined. The observed catalytic rate constants are indeed in agreement with the theoretical predictions. Other catalyst characteristics such as solubility and state of aggregation are, however, also of paramount importance in this reaction.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/jlac.199619961003
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    Polyether Catalysis of Ester Aminolysis - A Computational and Experimental Study (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1511-1522 
    Details
    ISSN: 0947-3440
    Keywords: Aminolysis ; Esters ; Catalysis ; Calculations, ab initio ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Model systems for the reaction of amines with esters were investigated with ab initio methods. Ammonia and methylamine were used as models for primary amines, and formic acid, methyl acetate, phenyl acetate, and p-nitrophenyl acetate were chosen to represent typical esters. Geometry optimizations were performed for all systems with the HF/6-31G** method, and relative energies were evaluated by using MP2/6-31G** single-point energies. The lowest barriers are found for the reaction of methylamine with p-nitrophenyl acetate. Reaction occurs in this case according to a direct displacement pathway, in which all bond formation and breaking occurs in a single step. Complexation of the transition structures by dimethyl ether or dimethoxyethane leads to much the same changes as observed for variation of the leaving group. Based on the ab initio data a force field for the calculation of transition state-catalyst complexation was developed. This force field as well as ground state complexation energies were employed to predict catalytic activities for a number of polyethers, polyalcohols, and pyrans, which in part, were also investigated experimentally.
    Additional Material: 12 Ill.
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    Die CuCl-katalysierte Reaktion von Trimethylsilyl(t-butyl)chlorphosphan mit Dimethylzirconocen: Ein Beispiel der Tandem-KatalyseProfessor Max Herberhold zum 60. Geburtstag gewidmet (1996)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 622 (1996), S. 2053-2056 
    Details
    ISSN: 0044-2313
    Keywords: Catalysis ; Diphosphanes ; 1,2-di-t-butyl-1,2-dimethyldiphosphane ; 1,2-di-t-butyl-1-chloro-2-methyl-diphosphane ; 1,2-di-t-butyl-1,2-dichloro-diphosphane ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The CuCl-catalyzed Reaction of Trimethylsilyl(t-butyl)chlorophosphane with Dimethylzirconocene: An Example for Tandem Catalysist-BuP(SiMe3)Cl was prepared from t-BuP(SiMe3)2 and hexachloroethane and reacted in situ with Cp2ZrMe2 in the presence of catalytic amounts of copper(I) chloride yielding t-Bu(Me)P—P(Cl)t-Bu (1) (2 : 1 reaction) or t-Bu(Me)P—P · (Me)t-Bu (2) (1 : 1 reaction) and Cp2ZrCl(Me). To understand the course of reaction, the reaction of dimethylzirconocene with CuCl and the decomposition of t-BuP(SiMe3)Cl in the presence of CuCl and tetrachloroethene were studied. The results suggest that CuCl reacts with t-BuP(SiMe3)Cl in the presence of C2Cl4 to give t-Bu(Cl)P—P(Cl)t-Bu (3); simultaneously, CuCl reacts with Cp2ZrMe2 with formation of methylcopper, which reacts with 3 to give 1 or 2, respectively.
    Notes: In situ aus t-BuP(SiMe3)2 und Hexachlorethan erzeugtes t-BuP(SiMe3)Cl reagiert mit Cp2ZrMe2 in Gegenwart katalytischer Mengen an Kupfer(I)-chlorid unter Bildung von t-Bu(Me)P—P(Cl)t-Bu (1) (2 : 1-Reaktion) oder t-Bu(Me)P—P(Me)t-Bu (2) (1 : 1-Reaktion) und Cp2ZrCl(Me). Zur Interpretation des Reaktionsverlaufs wurden die Umsetzung von Dimethylzirconocen mit CuCl sowie die Zersetzung von t-BuP(SiMe3)Cl im Gegenwart von CuCl und Tetrachlorethen untersucht. Demnach reagiert CuCl mit t-BuP(SiMe3)Cl in Gegenwart von C2Cl4 zu t-Bu(Cl)P—P(Cl)t-Bu (3); gleichzeitig bildet CuCl mit Cp2ZrMe2 Methyl-Kupfer, das mit 3 je nach Stöchiometrie zu 1 oder 2 reagiert.
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    Nonstabilized Alkyl Complexes and Alkyl-Cyano-Ate Complexes of Iron(II) and Cobalt(II) as New Reagents in Organic SynthesisAlkyliron and Alkylcobalt Reagents, Part 11. Part 10: ref. [1]. (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 386-403 
    Details
    ISSN: 0570-0833
    Keywords: alkylations ; catalysis cobalt compounds ; iron compounds ; Alkylation ; Catalysis ; Cobalt ; Iron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkyl transition metal reagents are being increasingly used for alkylations in organic synthesis. They have various advantages over alkyllithium and alkyl-magnesium reagents including higher selectivity, lower basicity, and - as long as the transition metal is not in its highest oxidation state - their willingness to undergo oxidative addition with electrophiles. Alkyl derivatives of FeII and CoII, which are not stabilized by special ligands but still can be easily handled, are in many cases superior to the well-known alkyl-CuI and -MnII reagents and can also undergo unexpected reactions. The introduction of alkyl-cyanoate complexes of FeII and CoII, the cyanide ligands of which (in contrast to neutral π-acidic ligands) do not reduce the reactivity, has led to further advances. Reaction mechanisms will be discussed and comparisons will be made with alkylating reagents containing CuI, MnII, NiII, or TiIV as well as with Pd-catalyzed coupling reactions. Furthermore, it will be shown that super-ate FeII complexes are almost certainly the reactive species in highly selective catalytic alkylations.
    Additional Material: 6 Tab.
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    Two-Metal Ion Catalysis in Enzymatic Acyl- and Phosphoryl-Transfer Reactions (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 2024-2055 
    Details
    ISSN: 0570-0833
    Keywords: catalysis ; enzymatic catalysis ; metallohydrolases ; Catalysis ; Enzyme catalysis ; Metalloenzymes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Numerous studies, both in enzymatic and nonenzymatic catalysis, have been undertaken to understand the way by which metal ions, especially zinc ions, promote the hydrolysis of phosphate ester and amide bonds. Hydrolases containing one metal ion in the active site, termed mononuclear metallohydrolases, such as carboxypeptidase. A and thermolysin were among the first enzymes to have their structures unraveled by X-ray crystallography. In recent years an increasing number of metalloenzymes have been identified that use two or more adjacent metal ions in the catalysis of phosphoryl-transfer reactions (R-OPO3 + R′-OH → R′-OPO3 + R-OH; in the case of the phosphatase reaction R′-OH is a water molecule) and carbonyl-transfer reactions, for example, in peptidases or other amidases. These dinuclear metalloenzymes catalyze a great variety of these reactions, including hydrolytic cleavage of phosphomono-, -di- and -triester bonds, phosphoanhydride bonds as well as of peptide bonds or urea. In addition, the formation of the phosphodiester bond of RNA and DNA by polymerases is catalyzed by a two-metal ion mechanism. A remarkable diversity is also seen in the structures of the active sites of these di- and trinuclear metalloenzymes, even for enzymes that catalyze very similar reactions. The determination of the structure of a substrate, product, stable intermediate, or a reaction coordinate analogue compound bound to an active or inactivated enzyme is a powerful approach to investigate mechanistic details of enzyme action. Such studies have been applied to several of the metalloenzymes reviewed in this article; together with many other biochemical studies they provide a growing body of information on how the two (or more) metal ions cooperate to achieve efficient catalysis.
    Additional Material: 34 Ill.
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    URL: http://dx.doi.org/10.1002/anie.199620241
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    Enantioselective C—C and C—H Bond Formation Mediated or Catalyzed by Chiral ebthi Complexes of Titanium and Zirconiumebthi = ethylenebis(tetrahydroindenyl).Dedicated to our mentor Professor Stuart L. Schreiber (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 1262-1284 
    Details
    ISSN: 0570-0833
    Keywords: asymmetric syntheses ; asymmetric catalysis ; enantiomeric resolution ; metallocenes ; sandwich complexes ; Asymmetric catalysis ; Asymmetric synthesis ; Chiral resolution ; Sandwich complexes ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of catalytic processes that effect enantioselective bond formation under mild conditions is an important and challenging task in modern chemical synthesis. In this connection, chiral C2-symmetric ansa-metallocenes (bridged metallocenes) have found notable applications as catalysts. This article discusses the chemistry of this class of chiral metallocene complexes with regard to their utility in catalytic and enantioselective C—C and C—H bond formation reactions. In addition, where applicable, a brief comparison with other related catalytic enantioselective processes is offered. Many of the reactions effected with high levels of enantioselectivity by catalytic amounts of these complexes are of great significance to the preparation of new materials and in the synthesis of therapeutic agents. For example, zirconocene complexes readily catalyze the enantioselective addition of alkylmagnesium halides to alkenes, and cationic zirconocene complexes may promote the highly stereoregulated copolymerization of terminal alkenes. Furthermore, the related chiral titanocenes are involved in an impressive range of useful asymmetric catalytic reactions, including the enantioselective hydrogenation of olefins and reduction of imines or ketones. This review attempts to bring together the practical aspects of the use of [(ebthi)M] complexes of Group 4 transition metals (catalyst synthesis and resolution), outline the manner in which the C2-symmetric chiral ligands are believed to initiate stereoselective bond formation, and highlight the aspects of this chemistry that are less well understood and require further research.
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    URL: http://dx.doi.org/10.1002/anie.199612621
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    Functionalized Diorganozinc Compounds: Key Reagents for the Synthesis of Enantiomerically Pure 2,5-Disubstituted cis- and trans-Tetrahydrofurans (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 1021-1028 
    Details
    ISSN: 0009-2940
    Keywords: Synthesis, stereoselective ; Catalysis ; Tetrahydrofurans ; Dialkylzinc reagents ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,4-Diol derivatives 4a-i were synthesized stereoselectively by either reagent- or catalyst-controlled routes using the addition of functionalized diorganozinc reagents to aldehydes. The stereoselectivities along the reagent-controlled synthetic path were in the range between 80:20 and 95:5. The stereoselectivities along the catalyst route exceeded 95:5. The 1,4-diol derivatives 4 thus obtained were transformed into enantiomerically pure cis- and trans-2,5-disubstituted tetrahydrofurans (16-20) by means of an intramolecular Williamson reaction.
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    A Molybdenum-Catalysed Electrocyclisation-Cycloaddition Sequence: Synthesis and Structure of a Pentacyclic Unsaturated Ketone (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 953-956 
    Details
    ISSN: 0009-2940
    Keywords: Molybdenum oxadiene complex ; Cycloaddition ; Catalysis ; Stereoselectivity ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pentacyclic unsaturated ketone 3 is obtained as the sole product by the reaction of pinocarvone (1) with cycloocta-triene in the presence of catalytic amounts of dicarbonyl-bis(η4-pinocarvone)molybdenum (2). Compound 3 formally resulting from a [4 + 2] cycloaddition reaction of bicy-clo[4.2.0]octa-2,4-diene with the alkene fragment of pinocarvone was characterised by means of spectroscopy (1H, 13CNMR, IR, MS) as well as by X-ray crystal structure analysis. A mechanism is proposed involving rigid molybdenum complexes as intermediates in order to explain the stereospecificity of the reaction.
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    A reinvestigation of the Meerwein-Ponndorf-Verley reduction A highly efficient variation using zirconium catalysts (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 677-683 
    Details
    ISSN: 0947-3440
    Keywords: Reductions ; Meerwein-Ponndorf-Verley reaction ; Catalysis ; Zirconium tetra-tert-butoxide ; β-Hydride shift ; Kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new variation of the Meerwein-Ponndorf-Verley reduction based on mechanistic considerations is presented. Under optimized conditions 1-(4-dimethylaminophenyl)ethanol was used as the reducing alcohol (2-4 equiv.), Zr(O-tBu)4 as the catalyst (0.2 equiv.), and toluene or cyclohexane as the solvent. Aldehydes and ketones (if not extremely sterically hindered) were reduced to the corresponding alcohols at room temperature mostly within 2-4 h in essentially quantitative yield. α,β-Unsaturated carbonyl compounds cleanly react in a 1,2-mode to afford the corresponding allylic alcohols.
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    URL: http://dx.doi.org/10.1002/jlac.199519950496
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    A new indicator electrode for oxygen sensors (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 471-475 
    Details
    ISSN: 1040-0397
    Keywords: Oxygen ; Sensor ; Catalysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical reduction of O2 was studied at Ni-Cu alloy electrodes in aqueous alkaline solution (0.1-6.0 M KOH) and in unbuffered neutral solution (0.1-2.0 M KCl) using the rotating disk electrode technique. Voltammetric measurements showed that the overall O2 reduction process at the electrodes containing 70-90% Cu is transport-limited at cathodic potentials, and that they can be used as indicator electrodes for galvanic-type oxygen sensors. An industrially produced Ni-Cu alloy “melhior”, which contains ∼ 30% Ni, was also studied, and this alloy proved to be an excellent O2 reduction catalyst. Melhior electrodes were utilized as indicator electrodes for oxygen sensors, and showed high output current stability and a long lifetime (exceeding one year).
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    The diastereoselectivity of zirconium alkoxide catalysed Meerwein-Ponndorf-Verley reductions (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1347-1351 
    Details
    ISSN: 0947-3440
    Keywords: Reduction ; Meerwein-Ponndorf-Verley reduction ; Catalysis ; Zirconium tetra-tert-butoxide ; Stereochemistry ; Diastereoselectivity ; Felkin-Ahn model ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new variation of the Meerwein-Ponndorf-Verley reduction using 1-[4-(dimethylamino)phenyl]ethanol (DMAPE) (6) or 1-tetralol (12) (3 equiv.) as the reducing alcohols and Zr(O-tBu)4 as the catalyst (0.2 equiv.) is kinetically controlled and highly stereoselective. Preferential axial attack is achieved with the sterically less bulky alcohol 6 in the case of 4-tert-butyl- and 3-methylcyclohexanones (1a → 96% axial and 3a → 93% axial attack). The combination tetralol (12)/Zr(O-tBu)4 behaves as a very bulky reducing agent, and the thermodynamically less stable alcohols 2c (80%) and 4c (92-96%) are formed preferentially in the reduction of 2a and 4b. The fused bicyclic systems 1-methyl-2-tetralone (14a) and flavanone (15a) and the steroids 16a-18a are reduced with high stereoselectivity to the corresponding cis alcohols 14b and 15b and the (β-alcohols 16b-18b. The stereochemical outcome is in agreement with the Felkin-Ahn model.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/jlac.1995199507179
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    Stereospecific Olefin Polymerization with Chiral Metallocene CatalystsDedicated to all those excellent graduate students who are the true heroes of this story (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 34 (1995), S. 1143-1170 
    Details
    ISSN: 0570-0833
    Keywords: alkenes ; catalysis ; metallocenes ; polymerizations ; Catalysis ; Metallocenes ; Polymerization ; Polyolefins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Current studies on novel, metallocenebased catalysts for the polymerization of α-olefins have far-reaching implications for the development of new materials as well as for the understanding of basic reaction mechanisms responsible for the growth of a polymer chain at a catalyst center and the control of its stereoregularity. In contrast to heterogeneous Ziegler-Natta catalysts, polymerization by a homogeneous, metallocene-based catalyst occurs principally at a single type of metal center with a defined coordination environment. This makes it possible to correlate metallocene structures with polymer properties such as molecular weight, stereochemical microstructure, crystallization behavior, and mechanical properties. Homogeneous catalyst systems now afford efficient control of regio- and stereoregularities, molecular weights and molecular weight distributions, and comonomer incorporation. By providing a means for the homo- and copolymerization of cyclic olefins, the cyclopolymerization of dienes, and access even to functionalized polyolefins, these catalysts greatly expand the range and versatility of technically feasible types of polyolefin materials.For corrigendum see DOI:10.1002/anie.199513681
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    Substituierte N,N-Chelat-Liganden - Anwendungen in der Molybdän-katalysierten Olefin-EpoxidationHerrn Prof. Dr. H. Schmidbaur zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2373-2379 
    Details
    ISSN: 0009-2940
    Keywords: Chelating ligands ; Molybdenum complexes ; Peroxo complexes ; Catalysis ; Olefine epoxidation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted N,N-Chelate Ligands - Applications in Molybdenum-Catalyzed Epoxidation of Olefins*Oxodiperoxomolybdenum complexes 4 of substituted 2-[3(5)-pyrazolyl]pyridines (2a-g) were synthesized in order to control the solubility of these complexes in organic solvents. Alkyl side chains (butyl, octyl, octadecyl) increase the solubility of the complexes and enable spectroscopic investigations in solution. Due to the symmetry of the ligands the peroxo complexes 4 appear in two isomeric forms, with the terminal oxo ligand in the trans position either to pyridine or to pyrazole. The latter isomer of (C5H4NC3H2N2CH2COOEt)MoO(O2)2 (4f) was characterized by an X-ray structure analysis. The alkyl-substituted peroxo complexes are active catalysts for the epoxidation of olefins with tert-butyl hydroperoxide.
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    Bimolekulare Radikalbildung durch H-Transfer, 7. Katalyse der Transferhydrierung von α-Methylstyrol durch 9,10-Dihydroanthracen mit 7H-Benz[de]anthracen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 691-696 
    Details
    ISSN: 0009-2940
    Keywords: Molecule-induced radical formation, kinetics of ; Catalysis ; ESR spectroscopy ; Radical clock ; Isokinetic relationship ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bimolecular Formation of Radicals by H-Transfer, 7[1].  -  Bimolecular Formation of Radicals via H-Transfer with Catalysis by 7H-Benz[de]anthraceneThe transfer hydrogenation of α-methylstyrene (2) by 9,10-dihydroanthracene (1) (DHA) with 7H-benz[de]anthracene (8) as a catalyst proceeds already at 210-260°C. Isotopic labeling, ESR spectroscopy, radical clock experiments, solvents effects, and thermochemical calculations support the postulated stepwise radical mechanism induced by bimolecular formation of radicals.
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    Ultratrace determination of molybdenum in the presence of 2-(2′-thiazolylazo)-p-cresol by catalytic-adsorptive stripping voltammetry (1994)
    Weinheim : Wiley-Blackwell
    Electroanalysis 6 (1994), S. 333-339 
    Details
    ISSN: 1040-0397
    Keywords: Molybdenim ; Adsorptive stripping voltammetry ; Catalysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The adsorptive collection of the molybdenum (VI) complex of 2-(2′-thiazolylazo)-p-cresok (TAC), coupled with the catalytic current of the adsorbed complex, yield an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were found with the use of a stirred acetate buffer (pH 2.9) supporting electrolyte, a TAC concetration of 1.0 × 10-5 M, and a concentration of 0.1 M potassium nitrate. In addition, a preconcentration potential of -0.13 V (vs. Ag/AgCl), equilibrium time of 30 seconds, and an anodic scan rate of 200 mV/s from -0. 93 to -0. 20 was used. A catalytic effect was observed when nitrate was present. The response was found to be linear over a concentration range of 0.0 to12.0 μg L-1 Mo (VI). For a preconcentration time of 3 minutes, the detection limit was found to be 11 pM. Possible interferences by anions and other trace metals were investigated. The interference by copper may be masked by CDTA, and sequential determination with molybdenum is possible. The merits of the procedure are demonstrated in the analysis of sea and mineral water.
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    Ligand-catalyzed metal ion reduction: Kinetics and analytical applications of nickel reduction catalyzed by nicotinamidePaper presented at the 4th International Symposium “Kinetics in Analytical Chemistry”, Erlangen, September 1992. (1994)
    Weinheim : Wiley-Blackwell
    Electroanalysis 6 (1994), S. 1051-1056 
    Details
    ISSN: 1040-0397
    Keywords: Nickel ; Nicotinamide ; Catalysis ; Polarography ; catalytic wave ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The catalytic reduction of Ni (II) in the presence of nicotihamide (NA) at pH 〈 7 was studied by direct-current and differential-pulse polarography (DPP). The prewave (with E1/2 around -0.78 V (versus saturated calomel electrode (SCE)) shows the typical behavior of an electrode process with regeneration of the reactant by a second-order, rate-determining chemical reaction. This reaction consists in the formation of the reducible nickel complex. The kinetics of the electrode process was studied by means of an adapted form of the equation derived by Koutecký for electrochemical reactions with a parallel chemical step. The rate constant for the formation of nickel-nicotinamide complex is slightly dependent en pH and buffer composition and ranges between 4.5 and 6.7 × 103 mole-1 L s-1. This electrode process enables the selective determination of Ni (II) in presence of a large excess of cobalt. For example, nickel impurity in cobalt salts can be determined by DPP, in acetate buffer (pH 4.6) containing 0.01 M nicotinamide and about 0.1 M cobalt salt sample.
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    Beschleunigung von Substitutionsreaktionen eines Phosphorsäurediesters durch Bis(guanidinium)-Verbindungen (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 49-58 
    Details
    ISSN: 0170-2041
    Keywords: Catalysis ; Guanidine ; Ion pair ; Phosphoric acid diester ; Staphylococcal nuclease, model of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acceleration of Substitution Reactions of a Phosphoric Acid Diester by Bis(guanidinium) CompoundsIon-pair coordination of phosphoric acid diesters with positively charged guanidines may cause large rate accelerations in substitution reactions. Here we present a comparative study on the catalytical influence of several mono- bis- and tris(guanidines) and of other cationic compounds. Large rate effects occur if 1,3-bis(aminomethyl)benzene or 1,2-ethylenediamine are used as spacers. Further acceleration can be achieved by exchanging guanidinium groups by 2-aminoimidazolines. The 4800-fold rate enhancement seen in the best case demonstrates the importance of the bis(guanidinium) moiety of staphylococcal nuclease and gives good perspectives towards future uses of guanidinium compounds as RNA cleaving agents.
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    Turning Points in CatalysisThis review is based on the opening lecture at the first European Congress on Catalysis (EUROPACAT-1), Montpellier, 12-17 September 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 913-937 
    Details
    ISSN: 0570-0833
    Keywords: Heterogeneous catalysis ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This personal journey through the enlarging landscape of heterogeneous catalysis, pure and applied, starts with the discovery in 1823 of a dramatic example of the synthesis of water that was to serve as the basis of the first commercial exploitation of catalysis, Dobereiners lighter (tinder box). The quickening pace of successive industrial innovations and of academic insight during the intervening 170 years are summarized and the turning points, both major and minor, identified. Although new concepts and new ideas emerged in relative profusion, few exhibited the longevity predicted for them at birth by their proponents. Some concepts, like broken milestones on a vanished road, have ceased to retain their significance. Some have survived, even flourished. But in catalysis, as in most other branches of natural science, new tools and new techniques, rather than new concepts, tend to hold sway. And just as experimental advances in enzymology and immunology have led to the design of remarkable new biocatalysts so also, but not yet at the same level of delicate control, have the tools and techniques of solid-state chemistry (including novel preparative and computational procedures), generated many powerful rationally designed inorganic catalysts.
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    URL: http://dx.doi.org/10.1002/anie.199409131
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    Bimolekulare Radikalbildung durch H-Transfer, 2. H-Transferreaktionen mit Phenalen (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1039-1045 
    Details
    ISSN: 0009-2940
    Keywords: Hydrogen transfer ; Radical formation, molecule induced ; C—H bond dissociation enthalpies, determination of ; Catalysis ; Coal pyrolysis ; Phenalene ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bimolecular Formation of Radicals by H-Transfer, 2[1]. - H-Transfer Reactions of PhenaleneThe uncatalysed H transfer from phenalane (7) to α1-methyl-styrene (2) and the selfreaction (d) of phenalene (7) are quantitative transformations in the presence of an excess of 9,10-dihydroanthracene (1) (DHA) in diphenyl ether at 200-250°C. In this system phenalene (7) is consumed only in reaction (d) because the phenalenyl radicals (9) are captured by DHA (1) to give phenalene (7) and 9,10-dihydroanthryl radicals (3). The latter disproportionate rapidly. Accordingly, phenalene (7) acts as a catalyst for the hydrogenation of α1-methylstyrene (2) by DHA (1). The activation parameters of the two reactions (e) and (d) were obtained from kinetic experiments between 200-250°C. They allow the determination of the C—H bond enthalpy δHdiss of phenalene (7) (65.3 kcal mol-1) at the methylene position.
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    Zur Synthese und Charakterisierung von Platincyclobutadien-Komplexen durch Reduktion von Hexachloroplatinsäure (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 2393-2396 
    Details
    ISSN: 0009-2940
    Keywords: Platinum complexes ; Cyclobutadiene complexes ; Alkyne dimerization ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Characterization of Platinumcyclobutadiene Complexes by the Reduction of Hexachloroplatinic AcidHexachloroplatinic acid is reduced in 1-butanol in the presence of an alkyne R-C≡C-R′ (R, R′ = Me, Et, nPr) to give platinumcyclobutadiene complexes [PtCl2(C4R2R2′)] (1). H[PtCl3(CH3CH2CH=CH2)] (2) is an intermediate which is isolated as bis(triphenylphosphoranylidene)ammonium salt (PPN-salt) [PPN][PtCl3(CH3CH2CH=CH2)] (3). The molecular structure of [PtCl2(C4Et4)] (1b) shows in the solid state a planar cyclobutadiene ring with internal bond angles of 93(3) and 87(2)°. The Pt-C bond lengths are 208(2) and 210(2) pm. The ethyl groups are pushed out of the ring plane, away from the Pt atom, with an angle of 7(2)°.
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    Darstellung und katalytische Eigenschaften von Rhodium(I)-Komplexsalzen des Typs [Rh(COD)o-Py(CH2)2P(Ph)(CH2)3ZR)]PF6 (Z = O, NH)Professor Dietrich Mootz zum 60. Geburtstage gewidmet (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 619 (1993), S. 1209-1213 
    Details
    ISSN: 0044-2313
    Keywords: Rhodium( I) Complex Salts ; Preparation ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation and Catalytic Properties of Rhodium(I) Complex Salts of the Type [Rh(COD)(o-Py(CH2)2 P(Ph)(CH2)3ZR)]PF6 (Z = O, NH).In dichloromethane solutions were reacted [Rh(COD)Cl]2 (COD = cis,cis-1.5-cyclooctadiene) with each of the four new ligands of the type o-Py(CH2)2P(Ph)(CH2)3ZR in the presence of the halogen scavenger TIPF6 at 0°C to complex salts [Rh(COD) (o-Py(CH2)2P(Ph)(CH2)3ZR]PF6 (ZR = OC2H5, I; OPh, II; NHPh, III; NHcyclo—C6H11, IV). The Rh1 complex cation in the obtained compounds I - IV coordinates besides the bedentate COD group the ligand donor atoms P und pyridinic N and the remaining donor atom Z is uncoodinated in an assumed square planar ligand geometry at the Rh central atom. In 1.4 dioxane solutions the complex catalysts I - IV polymerize at 25°C the substrate phenylacetylene (PA) to polyphenylacetylene (PPA): values of TON [h-1] between 352 (I) and 876 (IV), and average molecular weights Mw (GPC measurements) between 238 000 (I) and 199 900 (IV). These given values exhibit a dependency on the ZR group in complexes I - IV. The microstructure of isolated PPA is cis-transoidal. It is formed stereospezific and, based on MNDO calculations, is thermodynamically favoured. For the purpose of comparison, from both the newly synthesized compounds of the type [Rh(COD)DBN- (or DBU)Cl] (DBN = 1.5-Diazabi-cyclo[4.3.0.]non-5-en, DBU = 1.8-Diazabicycl0[5.4.0]- undec-7-en) was obtained a larger value of TON with 1292 (or 1327) [h-], but a lower value of M, with 166200 (or 131200). These catalysts including I -IV polymerize PA to PPA at a lower reaction temperature with improved selectivity and larger values of Mw as hitherto known catalyst systems.
    Notes: In Dichlormethanlösung wurde [Rh(COD)Cl]2 (COD = cis,cis-1.5-Cyclooctadien) mit vier neuen dreizähnigen Liganden vom Typ o-Py(CH2)2P(Ph)(CH2)3ZR in Gegenwart des Halogenfängers TIPF6 bei 0°C zu Komplexsalzen [Rh(COD)(o-Py(CH2)2P(Ph)(CH2)3ZR)] PF6 (ZR = OC2H5, I; OPh, II; NHPh, III; NHcyclo—C6H11, IV) umgesetzt. Das Rhodium-Komplexkation in den abgetrennten Verbindungen I - IV koordiniert aufgrund von 1H-, 31P-, 13C-NMR und IR-Meßergebnissen außer der zweizähnigen COD-Gruppe die Donoratome Phosphor und Pyridinstickstoff und läßt in der angenommenen quadratisch-planaren Koordinationsgeometrie ein vorhandenes Z-Donoratom ungebunden. Die Komplexkatalysatoren I - IV polymerisieren in 1,4-Dioxanlösung bei 25°C das Substrat Phenylacetylen (PA) zu Polyphenylacetylen (PPA): Werte für TON [h-1] von 352(I) und 876(IV) und mittlere Molmassen Mw (GPC-Meßresultate) zwischen 238 000(I) und 199 900(IV). Diese Werte der Lösungs-Fällungspolymerisation zeigen eine Abhängigkeit von der unkoordinierten ZR-Gruppe in Komplexen I - IV. Die Mikrostruktur des isolierten PPA ist cis-transoidal. Sie entsteht stereospezifisch und ist nach MNDO-Rechnungen die thermodynamisch begünstigte. Von den zu Vergleichszwecken dargestellten neuen Rhodium(I)-Komplexen des Typs [Rh(COD)DBN(bzw. DBU)Cl] (DBN = 1,5-Diazabicyclo[4.3.0]-non-5-en, DBU = 1,8-Diazabicyclo[5.4.0]undec-7-en) wird unter analogen Reaktionsbedingungen für PA ein höherer TON-Wert 1 292 (bzw. 1 327) [h-1], aber kleinerer Mw-Wert von 166 200 (bzw. 131 200) erhalten. Gegenüber bisher bekannten Katalysatorsystemen polymerisieren diese Komplexkatalysatoren einschließlich I - IV PA zu PPA bei milderen Reaktionstemperaturen, verbesserter Selektivität und höheren Mw-Werten.
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    URL: http://dx.doi.org/10.1002/zaac.19936190710
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    Amperometric response of mediating layers on electrode surfaces to Gaussian concentration profiles in flowing streams (1992)
    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 751-756 
    Details
    ISSN: 1040-0397
    Keywords: Catalysis ; flow analysis ; modified electrodes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model for a layer, containing catalytic centers, coated on an electrode and used for the mediation of analyte in a flowing stream is proposed and solved. The model applies to a situation of a Gaussian concentration profile of analyte impinging on the outer edge of the mediating layer. It was found that the important parameters that limit the current magnitude are the diffusion coefficient of the analyte through the layer, the effective electron diffusion coefficient through the layer and the rate of reaction between the mediator and the analyte. On evaluation of literature data, it was found that layers, high catalyst loading and with high rates of electron exchange, lead to linear peak current height versus concentration plots.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/elan.1140040803
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    Homogeneous catalysis of electrochemical reactions. Channel electrode voltammetry and the EC′ mechanism (1992)
    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 167-182 
    Details
    ISSN: 1040-0397
    Keywords: Catalysis ; reaction mechanism ; channel electrode ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The shape of the current-voltage curves at a channel electrode have been calculated for the various situations of the catalytic (EC′) mechanism. In particular the halfwave potential and limiting current are found to be highly sensitive to the solution-flow rate and to the concentrations of the mediator and substrate employed. These observations provide a ready method of unambiguously characterizing the different pathways.
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    URL: http://dx.doi.org/10.1002/elan.1140040207
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    Synthesis of Optically Active Bis(2-oxazolines): Crystal Structure of a 1,2-Bis(2-oxazolinyl)benzene ZnCl2 Complex (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 1173-1180 
    Details
    ISSN: 0009-2940
    Keywords: Bis(2-oxazolines) ; Chelating ligands ; Zinc complexes ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dinitriles (5-7, 12, 13) react with enantiomerically pure β-amino alcohols (8 - 11,17) under zinc chloride catalysis to give optically active C2-symmetric bis(oxazolines). 1,2-Bis(2-oxazolin-2-yl)benzenes 1a - e are obtained under mild reaction conditions. 1H-NMR spectroscopy indicates the formation of 1:1 complexes 23 of these compounds with ZnCl2. The energy required for a conformational interconversion of zinc dichloride complex 23e was determined by variable-temperature 1H-NMR studies. An X-ray structure analysis was performed with the substituted [1,2-bis(2-oxazolinyl)benzene]zinc dichloride complex 23a.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19911240532
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    Catalytic Air Blowing of Asphalt (1991)
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 63 (1991), S. 170-171 
    Details
    ISSN: 0009-286X
    Keywords: Air blowing ; Asphalt ; Catalysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cite.330630234
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    Catalytic ethylation of alkylbenzenes at high pressure (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 5 (1991), S. 167-172 
    Details
    ISSN: 0268-2605
    Keywords: Catalysis ; ethylation ; organosodium ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Study of the catalytic ethylation of p-t-butyltoluene in the presence of organosodium compounds, and of toluene in the presence of organopotassium compounds, was carried out at an ethylene pressure of 40 bar.Various yields of different products were obtained after 23 h of reaction in the presence of different tertiary polyamines used to complex and solubilize the organoalkali compounds.A higher initial ethylation rate was observed in the presence of organosodium than in the presence of organopotassium species. However, the thermal stability of organopotassium species being higher, much higher yields were observed in their presence in catalytic ethylation reactions than those observed previously.The results obtained concerning metallation or ethylation of hindered alkylaromatics may be interpreted by an anionic mechanism and the activation by a steric effect.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/aoc.590050305
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    1H and 13C NMR characterization of a new chiral porphyrin, meso-Tetra(α, β, α, β-o-camphanylamidophenyl)porphyrin, and its rhodium(III) complex (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 1084-1091 
    Details
    ISSN: 0749-1581
    Keywords: meso-Tetra(α, β, α, β-o-camphanylamidophenyl)porphyrin ; Rhodium complex ; Catalysis ; 1H and 13C NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a new chiral porphyrin, meso-tetra(α, β, α, β-o-camphanylamidophenyl)porphyrin, and its Mn(III) and Rh(III) derivatives is reported. Complete resonance assignments of both the 1H and 13C spectra of the ligand has been achieved via homo- and hetero-nuclear 2D NMR. Insertion of metal ions into the porphyrin ring was performed both in order to test the catalytic properties of the resulting complexes and to characterize the effect of of metal coordination on the spatial distribution of the bulky substituents. The Mn complex was then tested in catalytic chiral epoxidation reactions, giving low enantiomeric excesses (20%). The 2D NMR spectra of the Rh derivative indicate the existence of four molecular species generated by the interaction of the metal atom with the peripheral substituents of the porhyrin ring. In fact, a complex combination of axial coordination, together with the chirality of the camphanyl substituents, removed the symmetry of the porphyrin plane.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1260291103
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    Enantioselective Addition of Organometallic Reagents to Carbonyl Compounds: Chirality Transfer, Multiplication, and AmplificationParts of this review were presented by R. N. during his Merck-Schuchardt lecture series in the Federal Republic of Germany in May 1989. Ar represents aryl substituents in this article. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 49-69 
    Details
    ISSN: 0570-0833
    Keywords: Chirality transfer ; Carbonyl compounds ; Addition ; Enantioselectivity ; Synthetic methods ; Alcohols ; Reaction mechanisms ; Catalysis ; Alkylation ; Organometallic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic addition of organometallic reagents to carbonyl substrates constitutes one of the most fundamental operations in organic synthesis. Modification of the organometallic compounds by chiral, nonracemic auxiliaries offers a general opportunity to create optically active alcohols, and the catalytic version in particular provides maximum synthetic efficiency. The use of organozinc chemistry, unlike conventional organolithium or -magnesium chemistry, has realized an ideal catalytic enantioselective alkylation of aldehydes leading to a diverse array of secondary alcohols of high optical purity. A combination of dialkylzinc compounds and certain sterically constrained β-dialkylamino alcohols, such as (-)-3-exo-dimethylaminoiso- borneol [(-)-DAIB], as chiral inducers affords the best result (up to 99% ee). The alkyl transfer reaction occurs via a dinuclear Zn complex containing a chiral amino alkoxide, an aldehyde ligand, and three alkyl groups. The chiral multiplication method exhibits enormous chiral amplification: a high level of enantioselection (up to 98%) is attainable by use of DAIB in 14% ee. This unusual nonlinear effect is a result of a marked difference in chemical properties of the diastereomeric (homochiral and heterochiral) dinuclear complexes formed from the dialkylzinc and the DAIB auxiliary. This phenomenon may be the beginning of a new generation of enantioselective organic reactions.
    Additional Material: 19 Ill.
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    URL: http://dx.doi.org/10.1002/anie.199100491
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    Elementary Steps in Heterogeneous CatalysisFrom a paper presented at the awarding of the A-Mittasch Medal during a colloquium celebrating the 125th. anniversary of the founding of BASF on September 24, 1990 in Ludwigshafen (FRG). (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 1219-1227 
    Details
    ISSN: 0570-0833
    Keywords: Heterogeneous catalysis ; Reaction mechanisms ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Despite the great importance of heterogeneous catalysis, research in this field has long been characterized by its empiricism. Now, however, thanks to the rapid development of methods in surface physics, the elementary steps can be identified at the atomic level and the underlying principles understood. Defined single crystal surfaces are employed as models, based on the analysis of the surfaces of ‘real’ catalysts. Direct images, with atomic resolution, can be obtained using scanning tunneling microscopy, while electron spectroscopic methods yield detailed information on the bonding state of adsorbed species and the influence of catalyst additives (promotors) upon them. The successful application of this approach is illustrated with reference to the elucidation of the mechanism of ammonia synthesis. The catalyst surface is usually transformed under reaction conditions, and, as the processes involved are far-removed from equilibrium, such transformations can lead to intrinsic spatial and temporal self-organization phenomena. In this case, the reaction rate may not remain constant under otherwise invariant conditions but will change periodically or exhibit chaotic behavior, with the formation of spatial patterns on the catalyst surface.
    Additional Material: 20 Ill.
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    URL: http://dx.doi.org/10.1002/anie.199012191
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    Nickel: An Element with Wide Application in Industrial Homogeneous CatalysisDedicated to Professor Günther Wilke on the occasion of his 65th birthday (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 235-244 
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    ISSN: 0570-0833
    Keywords: Homogeneous catalysis ; Nickel ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The efficiency and future development of the chemical industry are closely linked to catalysis. It has been estimated, for example, that 60 to 70% of all industrial chemicals have involved the use of a catalyst at some point during their manufacture. In the past two decades the share of the market credited to homogeneous transition metal catalysis increasead to 10-15%. Besides cobalt, which is used mainly in hydroformylation reactions, nickel is the most frequently used metal. Many carbon-carbon bond formation reactions can be carried out with high selectivity if catalyzed by organonickel complexes. Such reactions include, inter alia, carbonylation reactions, cyclic and linear oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions. It was Reppe and Wilke who pioneered and shaped the field of homogeneous nickel catalysis. Great impetus was also given to the development of organonickel chemistry by Wilke and his students. Research in this area has contributed immensely towards an understanding of the reactions involved in catalysis. - This review is primarily concerned with nickel-catalyzed reactions which are of interest both preparatively and industrially; some mechanistic aspects are also dealt with.
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    URL: http://dx.doi.org/10.1002/anie.199002351
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    Intramolecular, Stoichiometric (Li, Mg, Zn) and Catalytic (Ni, Pd, Pt) Metallo-Ene Reactions in Organic Synthesis [New Synthetic Methods (75)]Dedicated to Professor Elias J. Corey on the occasion of his 60th birthday (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 38-52 
    Details
    ISSN: 0570-0833
    Keywords: Metallo-ene reaction ; Ene reaction ; Synthetic methods ; Catalysis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metallo-ene reactions, hardly recognized until very recently, have experienced a breathtaking development when applied in an intramolecular sense. Efficient regio- and stereoselective magnesium-ene cyclizations have served as a cornerstone for numerous syntheses of structurally diverse natural products (e.g., sesquiterpenes of marine or plant origin, alkaloids, fragrances, insect defense compounds, and a fungitoxin). A brilliant example is the synthesis of the elusive odorant (+)-khusimone which outshines 20 years of work in the field of tricyclovetivane synthesis. Palladium-, platinum-, and nickel-catalyzed versions of the metallo-ene reaction are in a comparatively early stage of exploration, but, nevertheless, reveal intriguing potential. Hence an almost 100% stereospecific C—O→C—;Pd-→ C—C chirality transfer permits simple and selective, cis- or trans-annelation processes. The mild cyclization conditions are compatible with various functional groups, such as nitrogen moieties, which offer interesting perspectives for the preparation of heterocycles (e.g., alkaloids) difficult to obtain by other methods. Carbon monoxide insertion reactions of the cyclized σ-metal intermediates were shown to afford annelated cyclopentanones and cyclopentenones with concomitant stereocontrolled formation of four carbon-carbon bonds. These and other observations, highlighted in this article, provide a platform for further extensions and applications of this powerful method in organic synthesis.
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    URL: http://dx.doi.org/10.1002/anie.198900381
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    Reaction Mechanisms in Heterogeneous Catalysis; C—H Activation as a Case Study (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 135-145 
    Details
    ISSN: 0570-0833
    Keywords: Reaction mechanisms ; Heterogeneous catalysis ; C-H activation ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterogeneous catalysis is changing from an empirical art to an exact science. The various methods for the analysis of solids and surfaces, constantly refined by materials science and surface science, seem to be almost unlimited. The increasing availability of atomic resolution microscopy as well as synchrotron radiation allows the characterization of catalyst particles, surface structures, surface processes and surface intermediates. We have learned to determine the surface structure sensitivity of catalytic reactions. Thermodynamic and kinetic data of catalytic reactions are now determined routinely. Isotopic exchange and labeling experiments provide information about reactant-catalyst interactions. How much have we learned through these techniques about the nature or mechanism of heterogeneously catalyzed reactions? The following article attempts to summarize the progress and the problems encountered in mechanistic studies of C—H bond formation and activation in a hydrogen atmosphere as an example for the present state of the understanding of reaction mechanisms in heterogeneous catalysis.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/anie.198901353
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    Solid Ion Conductors in Heterogeneous Catalysis (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 708-715 
    Details
    ISSN: 0570-0833
    Keywords: Solid ion conductors ; Ion conductors ; Heterogeneous catalysis ; Conducting materials ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical measurement of oxygen activity using ion-conducting solid electrolytes (λ-sensors) has become widely known, at least since the application of three-way catalysts in the postcombustion of exhaust gases from spark-ignition engines. However, the use of solid ion conductors is not limited to control devices. There are various other potential applications and numerous problems which can be studied: the formation of oxides in the course of catalytic reactions on metal surfaces, the improvement of selectivity and yield of catalytic reactions, such as the epoxidation of ethylene on silver catalysts and, finally, the cogeneration of electrical energy during oxidation reactions, such as the partial oxidation of methanol to formaldehyde.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/anie.198907081
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    Cyclizations via Palladium-Catalyzed Allylic Alkylations [New Synthetic Methods (79)] (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 1173-1192 
    Details
    ISSN: 0570-0833
    Keywords: Cyclization ; Allylic alkylation ; Alkylation ; Synthetic methods ; Palladium ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The history of ring systems in organic chemistry parallels their synthetic accessibility. Transition-metal-catalyzed cyclizations offer a new opportunity to create carbo- and heterocyclic compounds with great facility. Among these methods, allylic alkylations catalyzed by palladium have proven unusually productive because of the extraordinary chemo-, regio-, and diastereoselectivity and the continuing possibility for the development of enantioselectivity. The rules for ring closure differ from those for non-transition-metal-catalyzed reactions. A major benefit is the ability to generate medium (eight-, nine-, ten-, and eleven-membered) and large rings in preference to normal (five-, six- and seven-membered) rings. With the appropriate substrate, efficient macrocyclizations are possible under conditions of normal concentrations. A second major benefit derives from the complementary stereochemistry of the metalcatalyzed substitution (net retention of configuration) compared to non-metal-catalyzed reactions (inversion of configuration). Further, the requirement for the substrate to conform to the transition-metal template may impose a stereochemical preference in the intermediate that ultimately translates into the thermodynamically less stable organic product regardless of the stereochemistry of the starting material. While more work has focused on carbocyclic synthesis, the possibilities for heterocyclic synthesis are just beginning to be tapped. In addition to forming heterocycles by C—C bond formation, use of a heteroatom as a nucleophile has already proven effective for oxygen and nitrogen, with other nucleophiles awaiting investigation. New dimensions for cyclization via allylic alkylation arise by generating the requisite π-allylpalladium intermediates by methods other than palladium(0)-initiated allylic ionizations. In addition, metals other than palladium will clearly expand the possibilities, but as yet remain untapped.
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    URL: http://dx.doi.org/10.1002/anie.198911731
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    Dehydrogenative condensation of monohydrosilanes yielding disilanes in the presence of platinum complex catalysts (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 2 (1988), S. 91-92 
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    ISSN: 0268-2605
    Keywords: Catalysis ; dehydrogenation ; hydrosilane ; disilane ; platinum complex ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dimethylphenylsilane was catalytically dehydrogenated and condensed in the presence of platinum complexes to give 1,1,2,2-tetramethyl-1,2-diphenyl-disilane.
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    URL: http://dx.doi.org/10.1002/aoc.590020114
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    Electron-Transfer Chain Catalysis in Organotransition Metal ChemistryDedicated to Professor Jean Tirouflet (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 643-660 
    Details
    ISSN: 0570-0833
    Keywords: Catalysis ; Electrocatalysis ; Chain catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Parallel to organic electrocatalysis, the field of organotransition metal electrocatalysis has developed explosively since 1980. The theoretical and experimental foundations established by Feldberg in 1971 (ECE mechanism) have been applied, using fast electrochemical techniques, to various organometallic reactions such as isomerization, ligand exchange, chelation, decomplexation, and CO insertion and extrusion. Most of the work performed to date concerns ligand exchange reactions of N-donors and P-donors in mononuclear compounds, initiated by oxidants (or anodes) and of carbonyls and P-donors in clusters, initiated by reducing agents (or cathodes). The preparative aspects of electrocatalysis have already been impressively developed in cluster chemistry and indicate that the technique is extremely useful. This review first delineates the principles and characteristics of electrocatalysis applied in organotransition metal chemistry, and then, after outlining the choice of efficient initiating reagents, goes on to describe the systems up to August 1986.
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    URL: http://dx.doi.org/10.1002/anie.198806431
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