ISSN:0021-2148    

DOI:10.1002/ijch.199000030

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe natural bite angles of chelating diphosphine ligands have been determined by molecular mechanics calculations using the MACROMODEL program with a modified AMBER force field. The natural bite angle (βn) is defined as the preferred chelation angle determined only by ligand backbone constraints and not by metal valence angles. Potential energy diagrams for diphosphine chelates were constructed to estimate chelate flexibility. Molecular mechanics calculations have been used to select diphosphine ligands with natural bite angles of 120° for diequatorial chelation in trigonal bipyramidal metal complexe

ISSN:0021-2148    

DOI:10.1002/ijch.199000031

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractTwo alternative approaches for increasing the stereospecificity of Pd(0)‐catalyzed allylic etherification are presented, both of which also suppress product isomerization and elimination. One of them involves addition of chlorotrimethylsilane to a benzene reaction mixture. In the model reaction studied, it increases the ratio of the two stereoisomeric products, arising from either retention or inversion of configuration at the allylic carbon, from 3:1 to 9:1, respectively. The second approach involves the employment of both donor‐ and acceptor‐chelating ligands. Essentially 100% stereospecificity (retention of configuration) was achieved when the reaction was carried out in benzene at 60°C in the presence of Pd2(dba)3and bis‐1,2‐diphenylphosp

ISSN:0021-2148    

DOI:10.1002/ijch.199000032

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIdeas derived from topology and graph theory can be used to model the skeletal chemical bonding in metal carbonyl clusters as well as boranes and carboranes. In such molecules delocalized skeletal bonding occurs when there is a mismatch between the number of internal orbitals provided by a vertex atom and the number of polyhedral edges meeting at that vertex. Such global delocalization in deltahedral metal clusters may be regarded as a three‐dimensional analogue of the aromaticity in planar polygonal molecules such as benzene. Elementary graph‐theoretical considerations provide a basis for the 2n+2 skeletal electrons normally observed innvertex delocalized deltahedral metal clusters lacking tetrahedral chambers. Electron‐richn‐vertex metal clusters have more than 2n+ 2 skeletal electrons and form polyhedra having at least one face with at least 4 edges. Electron‐poorn‐vertex metal clusters have less than 2n+ 2 skeletal electrons and form deltahedra having at least one tetrahedral chamber. Ideas derived from group theory and graph theory can be used to analyze molecular orbital energy parameters for the most symmetrical deltahedral borane anions BnHn2−(particularlyn= 6 and 12) computed using either semiempirical extended Hückel methods or ab initio methods based on Gaussian orbitals. Some of the fundamental aspects of the graph‐theory derived models for skeletal bonding in delocalized deltahedral metal clusters are closely related to the tensor surface harmonic

ISSN:0021-2148    

DOI:10.1002/ijch.199000033

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractYb[N(SiMe3)2]2·2THF was found to desulfurize thiols (RSH) and dibenzyl sulfide. With thiols, the extent of desulfurization was a function of the relative stability of the corresponding radical, R·. Radicals were also involved in the desulfurization of dibenzyl sulfide. A unified mechanism involving a series of one‐electron redox steps leading to the generation of organic radical intermediates has been propo

ISSN:0021-2148    

DOI:10.1002/ijch.199000034

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

ISSN:0021-2148    

DOI:10.1002/ijch.199000035

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe ruthenium (II) diene complexes [Ru(X)(Cl)(nbd)(dppb)] (X = Cl, H; nbd = 2,5‐norbornadiene; dppb = PPh2(CH2)4PPh2) have been prepared and characterized spectroscopically. The X‐ray crystal structure of RuCl2(nbd)(dppb) (crystal data at 22°C: space groupP1,a= 10.896 (1) Å,b= 15.168(2) Å,c= 10.829 (1) Å, α = 103.02(1)°, β = 107.08(1)°, γ = 81.65(1)°,Z= 2,R= 0.054 for 6420 reflections) shows an octahedral geometry at Ru, with the chloro ligands slightly distorted from atransconfiguration (Cl)(1)‐Ru‐C1(2) = 168.4°); the unit cell contains two molecules of the complex and one molecule of benzene. Reaction of this complex with H2, in presence of Proton Sponge (PS, 1,8‐bis(dimethylamino)naphthalene) as base, is complicated by initial dissociation of nbd, and [Ru2Cl5(dppb)2]−‐PSH+is the major product. A minor product, the hydrido(diene) complextrans‐RuCl(nbd)(dppb)5, characterized spectroscopically, is more effectively synthesized from (a)trans‐Ru(H)Cl(nbd)(PPh3)2,1, and dppb, or (b) reaction of RuCl2(dppb)‐(PPh3) with H2in presence of nbd and PS. Complex5is unreactive toward H2or CO while1has been shown previously to give η2‐H2and norbornenoyl derivatives, respectively; the differ

ISSN:0021-2148    

DOI:10.1002/ijch.199000036

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract1,2,3‐Tri‐tert‐butyl‐3‐vinyl‐1‐cyclopropene6areacts with [RhCl(C2H4)]2to give the dimeric 1,2,3,5‐η‐pentadienediyl complex7a. The cyclopentadienyl derivative of this complex,8a, is obtained by reaction of7awith T1(C5H5). Crystal structures of both7aand8awere determined:7a; orthorhombic,Pbcn, a= 28.136 (4) Å, b = 10.637 (2) Å, c = 12.154 (2) Å,V= 3637.6 (1.2) Å3, and Z =4:8a; triclinic, P 1 ‐bar,a= 9.906 (2) Å,b =9.736 (2) Å,c= 12.126 (2) Å, α = 76.07 (2)°, β = 78.21 (2)°, γ = 65.34 (2)°,V= 1024.6 (3) Å3, andZ= 2. Treatment of7awith one equivalent of PMe3per Rh center results in regeneration of the vinylcyclopropene, demonstrating the reversibility of the ring opening reaction. Deuterium labelling studies show that both the ring opening and closing reactions proceed with retention of configuration at the vinyl olefin. Thus thetrans‐deuterated vinylcyclopropene6breacts with [RhCl(C2H4)2]2to give7bin which deuterium is located exclusively in thesynposition. Treatment of7bwith T1(C5H5) yields8b. Treatment of7bwith one equivalent of PMe3per Rh center results in formation of6bas the sole organic product. Unlike their triphenyl relative2, the tri‐Bu complexes7a,7b, 8a, and8bare stereochemically rigid in solution at room temperature, and do not undergo an η3→ η1→ η3isomerization on the NMR time scale. However, after prolonged heating,syn‐antisit

ISSN:0021-2148    

DOI:10.1002/ijch.199000037

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractCH2C(CH3)2CO2H free radicals react with Cu2+aqto form CuIII‐CH2C(CH3)2CO2H2+aq, which probably is rapidly transformed into intermediate I. This intermediate decomposes into Cu+aq+ CO2+ CH2=C(CH3)2. This is the first system in which a metal ion induced β‐carboxyl elimination reaction was observed. ·CH2C(CH3)2CO2H free radicals react with CuIII‐CH2C(CH3)2CO2H2+aqto form Cu2+aqand a mixture of (‐CH2C(CH3)2CO2H)2, (CH3)3CCO2H, and HOCH2C(CH3)2CO2H. CH2C(CH3)2CO2H reacts with Cu+aqto form CuII‐CH2C(CH3)2CO2H+aq. The latter intermediate decomposes both via homolysis and by a reaction with Cu2+aqto form 2Cu2+aq+ (CH3)3CCO2H. The spectra of the intermediates and the kinetics of reaction a

ISSN:0021-2148    

DOI:10.1002/ijch.199000038

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe synthesis and characterization of two tungsten carbonyl dimers containing bridging alkoxide or aryloxide ligands are described. The crystal and molecular structures of [PPN]2[W2(CO)8(OCH2CF3)2], 1, and [Et4N]3[W2(CO)6‐(OPh)3]‐CH3CN,2, are reported and compared with the structures of tetranuclear tungsten derivatives previously described. The dimer1crystalizes in the triclinic space groupP1 with unit cell parametersa= 13.460(11) Å,b= 12.318(5) Å,c= 13.842(10) Å, α = 82.73(5)°, β = 59.11(5)°, γ= 80.09(5)°,V= 1938(2) Å3, andZ= 1. The complex2crystalizes in the monoclinic space groupP21/nwith unit cell parametersa= 11.954(2) Å,b= 19.359(4) Å,c= 26.462(5) Å, β = 102.50(16)°,V= 5979(2) Å3,Z= 4. Molecular modeling software was utilized to construct a tetranuclear derivative from 1 similar to the structurally characterized [W(CO)3OH]4−4tetramer. The two tetramers were found to possess similar molecular parameters. This supports the contention that dimers of type 1 are the precursors of the tetramers. Comparisons of the tungsten alkoxides and aryloxides with the behavior of W(CO)6on

ISSN:0021-2148    

DOI:10.1002/ijch.199000039

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY