ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Organic Chemistry  (8)
  • bond activation  (2)
  • 1995-1999  (10)
  • 1960-1964
  • 1
    Electronic Resource
    Electronic Resource
    Two-State Reactivity in Organometallic Gas-Phase Ion ChemistryDedicated to Sir Derek H. R. Barton (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1393-1407 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In contrast to organic reactions, which can almost always be described in terms of a single multiplicity, in organometallic systems, quite often more than one state may be involved. The phenomenon of two states of different multiplicities that determine the minimum-energy pathway of a reaction is classified as two-state reactivity (TSR). As an example, the ion/molecule reactions of ‘bare’ transition-metal-monoxide cations with dihydrogen and hydrocarbons have been analyzed in terms of the corresponding potential-energy hypersurfaces. It turns out that, besides classical factors, such as the barrier heights, the spin-orbit coupling factor is essential, since curve crossing between the high- and low-spin states constitutes a distinct mechanistic step along the reaction coordinates. Thus, TSR may evolve as a new paradigm for describing the chemistry of coordinatively unsaturated transition-metal complexes. This concept may contribute to the understanding of organometallic chemistry in general and for the development of oxidation catalysts in particular.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780602
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Intermediacy of Proton-Bound Dimers and Ion/Dipole Complexes in the Unimolecular Decompositions of Dialkyl-Peroxide Radical Cations: Evidence for a coupled proton and hydrogen-atom transfer (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1999-2010 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unimolecular fragmentation reactions of the radical cations of diethyl, diisopropyl, dipropyl, isopropyl propyl, and di(tert-butyl) peroxide have been investigated by mass spectrometric and isotopic labeling techniques. Two competing pathways for unimolecular decomposition in the μs time regime (metastable ions) are observed: i) A combination of an α-C—C bond cleavage and a H migration gives rise to proton-bound dimers of two ketone or aldehyde molecules. ii) Ion/dipole complexes of alkyl cations and alkylperoxy radicals are generated by C-O bond cleavage. These complexes either exhibit direct losses of alkylperoxy radicals, or they rearrange via a coupled proton and H-atom transfer, this sequence of unprecedented isomerizations is completed by losses of alkyl radicals. Collisional activation experiments confirm that the ionic products of the latter process correspond to RR′C=OOH+; these ions can be regarded as protonated carbonyl oxides. In addition, we observe the elimination of alkenes leading to hydroperoxide radical cations and the expulsion of HO2⋅ radicals. The latter process implies a C—C bond formation step between the two alkyl fragments leading to higher alkyl cations.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780808
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Theory-enforced Re-investigation of the Origin of the Large Metal-Carbon Bond Strength in PdCH2I+ and its reactions with unsaturated hydrocarbonsIn [1], a preliminary account of the reaction of ground-state Pd+ with CH3I is given.Dedicated to Edgar Heilbronner on the occasion of his 75th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1110-1120 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: State-of-the-art ab initio studies demonstrate that the reaction Pd+ + CH3I → PdCH2I+ + H. is endothermic by ca. 20 kcal/mol, which translates into a bond dissociation energy (BDE) of ca. 83 kcal/mol for the Pd+—CH2I bond. This figure is in agreement with an experimental bracket of 68 kcal/mol 〈 BDE(Pd+—CH2I) 〈 92 kcal/mol. Based on these findings, the previously studied Pd+/CH3I system was re-investigated, and double-resonance experiments demonstrate that the formation of PdCH2I+ occurs stepwise via PdCH3+ as a reactive intermediate. Further, ion/molecule reactions of PdCH2I+ with unsaturated hydrocarbons are studied, which reveal the formation of carbon-carbon bonds in the gas phase.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790419
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    exo/endo-Selectivity in the Reaction of ‘Bare’ FeO+ with Bicyclo[2.2.1]heptane (Norbornane) (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1013-1019 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ‘Bare’ FeO+ reacts in the gas phase with norbornane with collision efficiency, and the most prominent cationic products correspond to [FeC5H6]+ (32%), [FeC7H8]+ (19%), [FeC3H6O]+ (19%) and [FeC6H6]+ (14%), which are structurally characterized by ligand exchange as well as collision-induced dissociation experiments. Circumstantial evidence is provided which indicates that the complexes [FeC5H6]+, [FeC7H8]+, and [FeC6H6]+ originate from an Fe(norbornene)+ intermediate which itself is formed by elimination of H2O from the [FeO(norbornane)]+ encounter complex. Although the reactions are preceded and/or accompanied by partial H/D exchange, the isotope distribution in the productions clearly points to a preferential endo-attack of bare FeO+, with an endo/exo-ratio of ca. 10.3 and kinetic isotope effects kH/kD for the endo-abstraction of 2.4 and of 7.7 for approaching an exo-C—H bond. The preferred endo-approach of bicyclo[2.2.1]heptane by ‘bare’ FeO+ is in distinct contrast to the P-450-mediated or the iron(III)porphyrin-catalyzed hydroxylation of this substrate which favor reactions at the exo-face.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780423
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Unparalleled, Enormous Metal-Carbon Bond Strength in PdCH2I+Dedicated to Albert Eschenmoser on the occasion of his 70th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1-5 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermalized Pd+ cations activate methyl iodide by selective cleavage of a C—H bond under formation of PdCH2I+ and an H-atom. This finding implies that the interaction energy between the metal cation and the CH2I fragment and thus the metal-carbon bond strength exceeds 103 kcal/mol. Theory predicts that the energetically most favorable isomer of this ion exhibits the Pd+—CH2—I structure, which is stabilized by an unprecedented bridging interaction between the two heavy atoms Pd and I.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790102
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Substituent Effects on Fe+-Mediated [4+2] Cycloadditions in the Gas Phase (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1205-1220 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Fe+-mediated [4+2] cycloaddition of dienes with alkynes has been examined by four-sector ion-beam and ion cyclotron resonance mass spectrometry. Prospects and limitations of this reaction were evaluated by investigating several Me-substituted ligands. Me Substitution at C(2) and C(3) of the diene, i.e., 2-methylbuta-1,3-diene, 2,3-dimethylbuta-1,3-diene, hardly disturbs the cycloaddition. Similarly, variation of the alkyne by use of propyne and but-2-yne does not affect the [4+2] cycloaddition step, but allows for H/D exchange processes prior to cyclization. In contrast, Me substituents in the terminal positions of the diene moiety (e.g., penta-1,3-diene, liexa-2,4-diene) induce side reactions, namely double-bond migration followed by [3+2] and [5+2] cycloadditions, up to almost complete suppression of the [4+2] cycloaddition for 2,4-dimethylhexa-2,4-diene. Similarly, alkynes with larger alkyl substituents (pent-1-yne, 3,3-dimethylbut-1-yne) suppress the [4 + 2] cycloaddition route. Stereochemical effects have been observed for the (E)- and (Z)-penta-1,3-diene ligands as well as for (E,E)- and (E,Z)-hexa-2,4-diene. A mechanistic explanation for the different behavior of the stereoisomers in the cyclization reaction is developed. Further, the regiochemical aspects operative in the systems ethoxyacetylene/pentadiene/Fe+ and ethoxyacetylcne/isoprene/Fe+ indicate that substituents avoid proximity.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800418
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Gas-Phase Reactions of Aliphatic Alcohols with ‘Bare’ FeO+ (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 123-132 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion/molecule reactions of ‘bare’ FeO+ with linear and branched aliphatic alcohols have been examined by Fourier-transform ion-cyclotron resonance mass spectrometry. Depending on the chain length of the alcohol, three different types of reactions can be distinguished: (i) Oxidation of the alcohols in the α-positions, to yield the corresponding carbonyl-Fe+ complexes, involves an initial O—H bond activation of the alcohol resulting in the formation of RO—Fe+—OH as the central intermediate. (ii) The formation of Fe(OH)2+, concomitant by loss of the corresponding neutral alkenes, competes with the generation of neutral OFeOH and a carbocation R+. These couples point to the existence of an intracomplex acid-base equilibrium and are connected with each other by a proton transfer from either acid to the other, e.g. i-C3H7+ + OFeOH⇄C3H6 + Fe(OH)2+. The process is driven by the Lewis acidity of FeO+ and starts with the abstraction of a hydroxide anion from the alcohol. (iii) For longer alcohols, e.g. pentanol, functionalization of non-activated C—H bonds which are remote from the O functionality is observed. Here, the OH group of the alcohol serves as an anchor, which directs the reactive metal-oxide cation toward a particular site of the hydrocarbon chain.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790113
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Catalytic gas-phase oxidation of olefins mediated by Fe(C6H6)+ and a comparison of Fe(L)+ complexes (L = benzene, pyridine, naphthalene) (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 429-431 
    Details
    ISSN: 0947-3440
    Keywords: Transition-metal ion chemistry ; Oxidation, gas-phase ; Catalytic reactions ; Ligand effects ; Fourier-transform ion cyclotron resonance mass spectrometry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The catalytic potential of Fe(L)+ complexes (L = benzene, pyridine, naphthalene) with respect to oxygen transfer to alkenes in the gas phase has been investigated by using Fourier-transform ion cyclotron resonance mass spectrometry. Oxidation of Fe(L)+ by N2O leads to Fe(L)O+ with reaction efficiencies of 86% (L = benzene), 40% (L = pyridine), and 44% (L = naphthalene), respectively. While „naked“ FeO+ behaves as a powerful CC- and CH-bond activation reagent, the ligated species Fe(L)O+ are entirely unreactive in that respect. However, oxygen transfer from Fe(L)O+ to olefins occurs at the collision rate with less than 10% formation of byproducts. Indirect evidence is presented suggesting that the O-atom transfer from Fe(L)O+ to olefins does not generate ketones or aldehydes; rather, epoxide formation is brought about. The largest turnover number (nt) is obtained for the Fe(C6H6)O+/C2H 4 system with nt = 6.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950253
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    C—H and C—C Bond Activation by Bare Transition-Metal Oxide Cations in the Gas PhaseDedicated to Michael Henchman and Rudolf Zahradnik (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 34 (1995), S. 1973-1995 
    Details
    ISSN: 0570-0833
    Keywords: bond activation ; gas-phase chemistry ; kinetics ; mass spectrometry ; transition-metal oxides ; C-H activation ; C-C activation ; Gas-phase reactions ; Mass spectrometry ; Transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Over the last decade the gas-phase chemistry of bare transition-metal oxide cations MO+ has received considerable attention. This interest is primarily due to the particular role of metal oxides in the oxidation of organic compounds in a variety of chemical and biochemical transformations. At a molecular level the simplest model system for these processes deals with reactions of bare metal-oxide ions in the gas phase. Due to the high oxophilicities of the early transition metals, their monoxide cations MO+ do not mediate O-atom transfer to any organic compounds at all. In contrast, monoxide cations of late transition metal can oxygenate a variety of hydro-carbons, and the most reactive ions, MnO+, FeO+, NiO+, OsO+, and PtO+, even activate methane. Insight into the reaction mechanisms of these oxidation processes can be obtained by analysis of reaction kinetics, isotope effects, product distributions etc., and for the reactions of MO+ with alkanes the initial C—H bond activation by MO+ is often rate-determining. Interestingly, the high reactivity of some MO+ ions is not always associated with a decrease in regioselectivity; for example, FeO+ ions induce regiospecific γ-C—H bond activation of dialkylketones in the gas phase. The situation for the epoxidation of olefins in the gas phase turns out to be even more complex than for condensedphase analogues. This is primarily because the metal ion that mediates O-atom transfer to the olefin also catalyzes the isomerization of the epoxides formed, to afford the energetically more stable aldehydes or ketones. Aromatic compounds can also be hydroxylated by MO+ ions, and particularly the oxidation of benzene by bare FeO+ ions in the gas phase reveals striking parallels to the metabolism of arenes. Furthermore, the storing capabilities of ion cyclotron resonance mass spectrometers even permit the design of catalytic processes in which a single metal ion converts more than one substrate molecule into an oxygenated product in a sequence of strictly bimolecular reactions. The most outstanding examples are the Pt+-mediated oxidation of methane by molecular oxygen and the Co+-mediated hydroxylation of benzene by N2O as oxidant. Finally, the key features of the gas-phase reactions are compared with observations in condensed-phase systems in which metal oxides are anticipated as central intermediates. The result of this comparison is promising in the sense that, in general, the understanding of transition-metal-mediated oxidations in the gas phase may lead to a more uniform description of these processes at a molecular level. Ultimately, it is hoped that gas-phase studies will serve as one of the building blocks in the evolution of tailor-made catalysts.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199519731
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Mechanism of the Fe+ Mediated C—C and C—H Bond Activations in Ethane from a Theoretical ViewpointThis work was supported by the Deutsche Forschungsgemeinschaft, the Volkswagen-Stiftung, and the Fonds der Chemischen Industrie. Computer time was generously provided by the Konrad-Zuse-Zentrum für Informationstechnik Berlin. We thank Prof. P. B. Armentrout and Dr. D. Schröder for helpful discussions and Prof. K. Morokuma for a preprint of ref. [12].Dedicated to Professor Paul von Ragué Schleyer on the occasion of his 65th birthday (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 34 (1995), S. 2282-2285 
    Details
    ISSN: 0570-0833
    Keywords: ab initio calculations ; bond activation ; density functional theory ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199522821
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...