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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of 5,5,10,10-tetramethyl-1-oxacyclotridecane-6,7,8,9-tetrone - on the mechanism of the Rubottom reactionDedicated to Professor Hans-Dieter Scharf on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1655-1661 
    Details
    ISSN: 0947-3440
    Keywords: Cyclic vicinal tetraketones ; Rubottom reaction ; Medium-sized rings ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 5,5,10,10-tetramethyl-1-oxacyclotridecan-6,7,8,9-tetrone (12) was achieved via a multistep procedure involving an oxidation known as the Rubottom reaction. The key intermediates were the dialdehyde (25), the diacid (33), the cyclic diketone (39) and the bis(silyl enol ether) (42). The oxidation of 42 with mCPBA yielded two diastereomers, the syn and anti bis(α-hydroxy ketones) (44, 45) the ratio of which depends strongly on the solvent used. This result combined with the isolation of the diepoxide (43) gives an insight into the stereochemistry of the Rubottom reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199509230
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation and Structures of Cyclotetradeca-4,11-diynone, Cyclotetradeca-4,11-diyne-1,8-dione, Their Exomethylene Derivatives, and 1,8-Dioxacyclotetradeca-4,11-diyneDedicated to Professor Gottfried Huttner on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1545-1550 
    Details
    ISSN: 0947-3440
    Keywords: Medium-sized rings ; Alkynes ; Conformation analysis ; Ketones ; Cyclizations ; Ether ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following 14-membered ring diynes have been synthesized: cyclotetradeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (6), the corresponding exomethylene derivatives 5 and 7, as well as 1,8-dioxacyclotetradeca-4,11-diyne (8). The synthesis of the diketal of 4 was achieved by the reaction of the ethylene ketal of 1,5-dibromopentan-3-one (9) with the dilithium salt of 1,8-nonadiyne. Similarly, the diketal of 6 was prepared from the dilithium salt of the ethylene ketal of 1,8-nonadiyn-5-one 11 with 9. The unprotected ketones 4 and 6 were obtained by treating the ketals 10 and 14, respectively, with HCl. The ketones 4 and 6 were transformed to the exomethylene derivatives by a Wittig reaction. The reaction of the dilithium salt of 5-oxanona-1,8-diyne (16a) with 1,5-dibromo-3-oxapentane (15) yielded 8. X-ray investigations of single crystals of 6 and 8 revealed chair conformations with a zig-zag arrangement, employing two anti orientations of the two chains between the triple bonds. A zig-zag arrangement of the chain containing the carbonyl group was also found in 4. In 3b and 7 Ci symmetry was found, with only one anti conformation in each chain. Molecule 6 crystallizes with C2h symmetry and 8 with a center of symmetry.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970734
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis and Properties of 4,4,9,9-Tetramethyl-1-oxa-cycloundecane-5,6,7,8-tetrone and 5,5,10,10-Tetramethyl-1-oxa-cyclotridecane-6,7,8,9-tetroneDedicated to Professor Richard Neidlein on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 271-277 
    Details
    ISSN: 0947-6539
    Keywords: biomineralization ; medium-sized rings ; calcite ; crystal morphology ; glycoproteins ; polysaccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 4,4,9,9-tetramethyl-1-oxa-cycloundecane-5,6,7,8-tetrone (9) and 5,5,10,10-tetramethyl-1-oxa-cyclotridecane-6,7,8,9-tetrone (10) has been achieved in a multistep procedure. The key steps in this synthesis were the ring closure of 23 and 24 to 25 and 26, respectively, and the oxidation of the triple bond with RuO2/NaIO4 to the dihydroxydiketones 31 and 32. Compound 9 is the first cyclic tetraketone for which an intramolecular donor-acceptor stabilization has been found. A strong transannular interaction between the ether oxygen and the C4O4 unit in 9 was detected by X-ray studies on single crystals of 9. The transannular distance is 2.7-2.8 Å. Further evidence for a strong transannular interaction was obtained from the comparison of the reduction potential and the first band in the UV/Vis spectrum with the corresponding values from other openchain tetraketones. These findings were substantiated by PE investigations on 9. The crystal structures of the dihydroxy-diketones 31 a and 32 a showed that, in the case of the eleven-membered ring (31 a), there are also short transannular distances between the ether oxygen and the C2O2 moiety (2.5 Å and 2.9 Å). In the case of the thirteen-membered ring (32 a), no transannular interactions were found in the solid state.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020307
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum-Chemical Investigations of Stabilizing Interactions in μ-Diborylcarbene Dicobalt Complexes with a Planar Tetracoordinate Carbon AtomDedicated to Professor Gerhard Herberich on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 294-299 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; cobalt ; planar carbon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum-chemical methods have been employed to study the nature of stabilization in dinuclear cobalt complexes of the general formula [{(C5H5)Co}2(μ-CR12BCBR2R3)] (6) as well as the “antivan't Hoff-Le Bel” configuration of the planar tetracoordinate carbon (ptC) atom of the bridging diborylcarbene ligand 9. Extended Hückel and ab initio Hartree-Fock calculations have been carried out for the model compounds 6b (R1 = R2 = R3 = H) and 6c (R1 = R2 = H; R3 = C6H5). Ab initio electron deformation density maps and natural population analysis calculations show that complexes 6 are stabilized through push-pull effects by which the ptC experiences π electron density delocalization and σ electron density accumulation. The calculated electronic configuration of the ptC in the free ligand 9b is σ2.978π1.501, and in 6b σ3.944π1.356. Electron density donation from one cobalt atom to an aryl group on the bridging ligand further contributes to the stabilization of the complexes 6.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030219
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  • 5
    Electronic Resource
    Electronic Resource
    Electron-poor 2,3-Dihydro-1,3-Diborolyl Complexes of Iron and Ruthenium: Synthesis, Reactivity, and Crystal and Electronic Structures of an Iron Sandwich ComplexDedicated to Professor Herbert Schumann on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 487-494 
    Details
    ISSN: 0947-6539
    Keywords: boron compounds ; diboroles ; Group 8 complexes ; sandwich complexes ; semi-empirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition product of sodium hydride and the 2,3-dihydro-1,3-diborole (CiPr)2(BEt)2CHMe (3c) reacted with [{(C5Me5)FeCl}x] to produce the green sandwich complex [(C5Me5)Fe{n5-(CiPr)2(BEt)2CMe}] (2 c), which formally contains 16 valence electrons (VE). Complex 2c has unexpected structural properties in the solid state: the 1,3-diborolyl ring is extremely folded (41°), and the Fe-C2 distance is short (1.90 Å). Analogously, violet Ru complexes 4a,c,d were obtained from 3a,c, NaH or tBuLi, and [{(C5Me5)RuCl}4]. With the less bulky heterocycles 3 b,e the new 30 VE triple-decker complexes [(C5Me5)Ru{μ,n5-(CR1)2(BR2)2CMe}RuH(C5Me5)] (5b,e) were formed, which contain a Ru-H bond. Cyclic voltammetric studies revealed the existence of stable anions 2c- and 4d- formed by reversible one-electron reduction at -1.26 and -1.40 V, respectively (vs. SCE). The red-brown anions were further characterized by ESR spectroscopy following stepwise reduction of the neutral species with potassium in THF. Addition of CO to 4a and 4d led to formation of the monocarbonyl complexes [(C5Me5)Ru(CO){n5-(CR1)2-(BR2)2CMe}] (6a,d), and 6d was characterized by X-ray structure analysis. The heterocycle in 6d is less folded (19°) than in 2 c. Its CO ligand causes a 28.5° tilt of the cyclic ligands. Reaction of CO with 2 c yielded a red product of unknown structure. The electronic structure of 2 was studied by EH-MO theory, which revealed a unique bonding in the sandwich. The s̰ electron density of the B-C bonds participates in the bonding to the iron atom; this demonstrates that the number of bonding electrons is the same as in ferrocene. Thus, the complexes 2 actually have 18 VE.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020506
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  • 6
    Electronic Resource
    Electronic Resource
    Through-Bond Interactions in Silicon-Phosphorus and Silicon-Arsenic Compounds: A Facile Synthesis of Dodecamethyl-2,3,5,6,7,8-hexasila-1λ3,4λ3-diphosphabicyclo[2.2.2]octane, Its Arsenic Analogue, and Related Compounds (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 874-880 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; arsenic ; silicon ; phosphorus ; photoelectron spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dodecamethyl-2,3,5,6,7,8-hexa-sila-lλ3,4λ3-diphosphabicyclo[2.2.2]oc-tane (1) and its arsenic analogue 2 are readily accessible in 69 and 73% yield, respectively, by the cyclocondensation reaction of 1,2-dichloro-1,1,2,2-tetrame-thyldisilane (5) with the lithium pnictides [LiEH2(dme)] (E = P (6), As(7); dme = 1,2-dimethoxyethane). The reactions proceed via 1,4-diphosphaoctamethyltetrasi-lacyclohexane (8) and its arsenic analogue 9, respectively, which were isolated and structurally characterized by X-ray crystallography. The molecular structures of 1 and 2, which are isotypic, were also established by single-crystal X-ray analysis: they possess D3 point symmetry with the expected Si-E bond lengths (E = P, As) but unusually long Si-Si bonds. The latter are 0.02-0.03 Å longer than those in 8 and 9, mainly due to through-bond interactions (TB) between donating n orbitals of the E atoms and the σ* acceptor orbitals of the Si-Si bond. The first expanded analogues of 1, namely, 12 and 14, with hexamethyltrisilane and dodecamethyl-hexasilane chains bridging the two phosphorus atoms, were synthesized in a onepot cyclocondensation reaction of the corresponding 1,3- and 1,6-dichloro-oligosilanes 11 and 13, respectively, with [LiPH2(dme)]6. Ab initio calculations on the parent compounds 1a, 12a, and the second-row analogue 1,4-diazabicyclo-[2.2.2]octane (B) were carried out in order to analyze the different coupling constants and magnitudes of intramolecular interactions (through-space/through-bond coupling). TS and TB coupling in B were found to be about two times stronger than in the congener 1a, due to the compactness of the N2C6 skeleton and the greater extent of s, p hybridization at nitrogen. Evidence for TB interactions in 1 was obtained by photoelectron spectroscopy and by comparison of the two first vertical ionization potentials with calculated values for 1a. The best agreement with experimental data was achieved when 1a was calculated at the MP2 level. Compound 1a preferentially adopts D3 point symmetry; the higher-symmetry D3h form possesses one imaginary frequency and is slightly less stable (0.46 kcal mol-1 at HF/6-31 G*//HF/6-31 G* and 1.58 kcal mol-1 at MP2/ 6-31 G*//HF/6-31 G* level), suggesting that this structure corresponds to a transition state on the potential energy surface. The structures corresponding to the global minimum of B and 12a have D3h and C3h symmetry, respectively. At the HF/6-31 G*//HF/6-31 G* level the D3h form of 12a is 17.61 kcal mol-1 less stable than the C3h minimum.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030607
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  • 7
    Electronic Resource
    Electronic Resource
    Replacement of One CO Unit in Dicarbonyl(η5-cyclopentadienyl)cobalt Derivatives by Bis(tert-butylsulfonyl)acetylene (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 629-632 
    Details
    ISSN: 1434-1948
    Keywords: Alkyne complexes ; Carbonyl complexes ; Cobalt ; CO replacement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of dicarbonyl(η5-cyclopentadienyl)cobalt (1) and some of the Cp-ring substituted congeners with bis(tert-butylsulfonyl)acetylene (BTSA) results in the replacement of one CO group by the BTSA moiety. The variation of the yields and reaction times indicates a dependence of the reactivity of 1-6 with BTSA as a function of substituents. X-ray investigations of the products show that the alkyne unit is strongly bound to the metal.
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  • 8
    Electronic Resource
    Electronic Resource
    Structure of 2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene and of 2,4-Di-tert-butyl-1,3-diphosphabenzene: X-ray Analysis, Photoelectron Spectra and Molecular Orbital Calculations (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1619-1621 
    Details
    ISSN: 1434-1948
    Keywords: 1,3,5-Triphosphabenzene ; 1,3-Diphosphabenzene ; Photoelectron spectroscopy ; Molecular orbital calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene (1) as well as the He(I) photoelectron spectra of 1 and 2,4-di-tert-butyl-1,3-diphosphabenzene (2) have been investigated. It was found that 1 is planar with average C-P-C angles of 109.3° (±0.3°) and P-C-P angles of 130.7° (± 0.4°). All P-C bond lengths amount to 1.727 (± 0.008) Å. The PE spectra were interpreted by comparison with the results of ab initio calculations (RHF/ 6-31G*). They reveal a splitting of the lone pairs on P in 2 of 0.7 eV.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Reactions of 1,8-Diheterocyclotetradeca-4,11-diynes with (η4-Cycloocta-1,5-diene)(η5-cyclopentadienyl)cobalt (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 499-504 
    Details
    ISSN: 1434-1948
    Keywords: Alkynes ; Heterocycles ; Cyclizations ; Cobalt ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following monocyclic and bicyclic 14-membered diynes were treated with [CpCo(cod)]: 1-oxacyclotetradeca-4,11-diyne (2), 1,8-dioxacyclotetradeca-4,11-diyne (3), cyclotetradeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (5), 1,1,8,8-tetramethyl-1,8-disilacyclotetradeca-4,11-diyne (6), 1-allyl-1-azacyclotetradeca-4,11diyne (7), 1,8-dipropyl-1,8-diazacyclotetradeca-1,11-diyne (8), 1,8-diallyl-1,8-diazacyclotetradeca-4,11-diyne (9), 1,8-diazabicyclo[6.6.4]octadeca-4,11-diyne (10), 1,8-diazabicyclo[6.6.6]eicosa-4,11-diyne (11), 1,10-diazabicyclo[8.6.6]docosa-13,19-diyne (12) and 1,12-diazabicyclo[10.6.6]tetracosa-15,21-diyne (13). In all cases we obtained an intramolecular cyclobutadiene complex stabilized with a CpCo fragment (15-26). For 3 we could isolate, besides the cyclobutadiene complex 16, the trimerization product 28. In the cases of 15, 16, 18, 20, 23, 25, and 26 the structure of the cylobutadiene complexes could be confirmed by X-ray studies. Common to all structures is a boat-like conformation of the tricyclic unit containing the cyclobutadiene ring. The two cycloheptene units adopt a chair conformation in which the heteroatom is removed from the metal center.
    Additional Material: 1 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis of Tetraborylethenes and 1,1,1′,1′-Tetra- and Hexaborylethanes; Electronic Interactions in Tetraborylethenes and 1,1,1′,1′-Tetraborylethanes, and HF-SCF Calculations (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1693-1700 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Homogeneous catalysis ; Ab initio calculations ; Donor-acceptor systems ; X-ray analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The catechol-substituted diboranes(4) 1 react with the catechol-substituted diborylacetylenes 2, in the presence of [Pt(PPh3)2(C2H4)] or [Pt(PPh3)4], to give tetra- and hexaborylethane derivatives. When [Pt(cod)2] is used as catalyst, the tetraborylethene 5a is formed exclusively. Catalytic hydrogenation of 5a affords the 1,1,1′,1′-tetraborylethane 4a, which has been studied by an X-ray structure analysis. Natural Bond Orbital (NBO) analyses for the RHF/3-21G optimized geometries of 4a and 5a reveal intramolecular stabilization of the boron pz orbital. This covers B-O, B-B, and agostic interactions. The photoelectron spectrum of 5a is reported
    Additional Material: 7 Ill.
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