ISSN:0009-2940    

DOI:10.1002/cber.19951281018

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe first five‐membered titanacyclic cumulene (5) was prepared by treatment of the titanocene generator Cp2Ti(Me3SiC2SiMe3) with the di‐tert‐butylbutadiyne in a molecular one‐to‐one ratio. The reaction of5with “Cp2Zr” or of the analogous complex with “Cp2Ti” leads to cleavage of the central C‐C bond in the metallacyclocumulene complexes to afford the same product, the heterodimetallic ρ, π,‐alkynyl‐bridged titanocene‐zirconocene complex Cp2Zr(μ‐η1η2‐C≡CtBu)Cp2Ti(μ‐η1η2‐C≡CtBu) (6), in which each alkynyl group is π‐bonded to one and π‐bonded to the other metal as shown by X‐ray diffraction studies. In solution the two alkynyl groups become equivalent. The coupling reaction of “Cp2Ti” with bis(trimethylsilyl)butadiyne in a one‐to‐two molecular ratio leads

ISSN:0009-2940    

DOI:10.1002/cber.19951281002

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe insertion of the alkynes ZC≡CZ (2a‐i) [Z = Co2R: R = Me (a), Et (b),nPr (c),iPr (d),nBu (e),tBu (f),neo‐Pent (g),cyc‐Hex(h); Z = CF3(i)] into the P1‐P2bond of the diphos‐phamolybdacyclopropane Mes (1) (Mes = 2,4,6‐trimethylphenyl) results in the formation of the diphosphamolybdacyclopentenes Mes (3a‐i). According to an X‐ray structural analysis,3acrystallizes in the space groupP21/cwith the mesityl function at P2and the cyclopentadienyl fragment at the metal atom on the opposite side of the planar five‐membered ring. The same orientation is found in solution by NMR experiments (NOE; 2D1H,13C HETCOR). Kinetic investigations confirm that the rate constants decrease in the sequence R = Me>Et>nPr>isoProp>Cy>nBu>neo‐Pent>tBu. The second‐order reaction and the strongly negative activation entropy which was determined in the case of the reaction1+2e→3eare consistent with a nucleophilic attack of P2at one of the triply bonded carbon atoms of the alkyne. The reaction of3a, hwith sulfur affords the diastereomeric compounds Mes (4a, h). An X‐ray structural analysis of the heterocycle4h, which crystallizes in the space groupP1, shows the presence of the enantiomeric pair SR/RS. The reaction of1with alkynes is hindered if this heterocycle is oxidized by sulfur to give Mes (5). Further reaction of5with sulfur leads to the ring‐expanded heterocyclic intermediate (6) which crystallizes in the space groupP1. The five‐membered ring in6has an envelope conformation. Upon thermally induced cleavage of the P2S2Mes fragment from6the three‐membered ring (

ISSN:0009-2940    

DOI:10.1002/cber.19951281003

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractAlthough tetrakis(2‐tert‐butyl‐4,5,6‐trimethylphenyl)distannene (9), the first tetraaryl‐distannene to be reported on, is stable in the solid state, only the monomeric stannylene8can be detected in solution. An X‐ray crystal structure analysis of9reveals a long tin‐tin bond length of 291.0(1) pm and atrans‐bent Sn2C4framework with different fold angles of

ISSN:0009-2940    

DOI:10.1002/cber.19951281004

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractEthynylcyclopropanecarboxylic acid esters2c/2twere prepared from phenylbutenyne1and ethyl diazoacetate. Pure diastereomers were obtained by chromatography and converted into the corresponding acyl chlorides4c/4t.Reaction with K2[M(CO)5] (M = Cr, W) affords alkynylcyclopropylcarbene complexes of chromium7c/7tand tungsten8c/8t.An X‐ray structure analysis of7treveals a distorted cyclopropane skeleto

ISSN:0009-2940    

DOI:10.1002/cber.19951281005

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPhosphaalkynes2undergo cocyclooligomerization reactions with the phosphinidene14or the phosphinidene‐W(CO)5complex18to furnish the phosphorus‐carbon cage compounds16or23.The phosphinidene14is generated by the thermal reaction of2a‐cwith the phosphole11, a process in which the initially formed 7‐phosphanorbornadienes12a‐cdecompose to the λ3‐phosphinines13a‐cand the desired reactive intermediate. When three further equivalents of the phosphaalkynes2a‐care employed, the tetraphosphahomoquadricyclanes16a‐ccan be isolated in 53‐65% yields. The second approach is based on the thermal fragmentation of17to generate the phosphinidene‐W(CO)5complex18which, in turn, reacts with four equivalents of the phosphaalkynes2aorbto produce the pentaphosphadeltacyclanes23aorb.The constitutions of these novel phosphorus‐carbon cage compounds were confirmed by X‐ray crystal stru

ISSN:0009-2940    

DOI:10.1002/cber.19951281006

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe molecular structures of XMg(A1H4) · 4 THF (1a, 2, 3a) (X = A1H4, Cl, Br) have been determined by X‐ray structural analysis. Each compound possesses a hexacoordinated Mg center and AlH4−groups bound to this center via a single hydride bridge bond. Attempts to prepare ROMg(AlH4) compounds were successful only for sterically demanding groups R (R = CMe3, CPh3, naph, mes, smes). The 2‐naphthoxy derivative7, a compound with the composition (naphO)Mg‐(AlH4) · 2.5 THF, is a dimer with a central Mg2O2ring. One of its two AlH4−groups is terminally bound to one Mg atom, the other bridges the two Mg centers. This structure indicates how AlH4−transfer may occur from ROMg(AlH4) compounds to form Mg(OR)2

ISSN:0009-2940    

DOI:10.1002/cber.19951281007

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reaction of [Mo(CO)4(C7H8)] (1) with I2gave the norbornadienemolybdenum(II) complex [Mo(CO)2(C7H8)I2]n≥1(2), which existed in an equilibrium of two isomeric forms. In acetonitrile,2reversibly formed the adduct [Mo(CO)2‐(C7H8)(NCCH3)I2] (3), whereas on treatment with 2,2′‐bipyridine or 4,4′‐di‐2,2′‐tBu‐bipyridine, it gave stable 7‐coordinated molybdenum(II) complexes, [Mo(CO)(C7H8)‐(C10H8N2)I2] (4) and [Mo(CO)(C7H8)(C10H6tBu2N2)I2] (5), in good yield. In similar reactions, the related dibromomolybdenum compounds [Mo(CO)(C7H8)(C10H8N2)Br2] (6) and [Mo‐(CO)(C7H8)(C10H6tBu2N2)Br2] (7) were prepared by oxidation of1with two equivalents of CuBr2. The X‐ray structural analysis of6reveals that the geometry around the molybdenum atom is nearly perfectly pentagonal bipyramidal, with the CO and one of the bipyridyl rings perpendicular to the plane formed by the other ligands. The compounds5and6react with AgSbF6by halogen abstraction to give cationic complexes, {[Mo(CO)(C7H8)(C10H8N2)Br]SbF6}n≥1(8) and {[Mo(CO)(C7H8)(C10H6tBu2N2)I]SbF6}n≥1(9): In acetone,8and9reversibly formed the adducts [Mo(CO)(C7H8)(C10H8N2)(acetone)Br]SbF6(8′) and [Mo(CO)(C7H8)(C10H6tBu2N2)(acetone)I]SbF6(9′); while on treatment with PMe3, the stable monomeric complexes, [Mo(CO)(C7H8)(C10H8N2)(PMe3)Br]SbF6(10) and [Mo(CO)(C7H8)(C10H6tBu2N2)(PMe3)I]SbF6(11), were isolated in almost quantitative yield. In the presence of KBr, compound8′reverted to the dibromo complex6, whereas9′ reacted to produce a 1:1:2 mixture of5, 7and the bromo(iodo) complex [Mo(CO)(C7H8)(C10H6tBu2N2)BrI] (12). The same mixture is available from

ISSN:0009-2940    

DOI:10.1002/cber.19951281008

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPhosphoniumylidyl thioxophosphanes and selenoxophosphanes, the only known monomeric chalcogenoxophosphanes, react in a 2:1 ratio with triphenylphosphonium ylides. With loss of PPh3the 1,2,4‐thia(or selena)diphosphetane monosulfides (or selenides) are formed. Their prominent structural feature are the very different PS bond lengths in the ring. They can be oxidized to the corresponding disulfides or sulfide selenides. The latter rearrange to the isomer in which the selenium atom has become a ring membe

ISSN:0009-2940    

DOI:10.1002/cber.19951281009

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

Abstract1,4‐Diol derivatives4a‐iwere 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 derivatives4thus obtained were transformed into enantiomerically purecis‐andtrans‐2,5‐disubstituted tetrahydrofurans (16‐20) by means of an intramolecular

ISSN:0009-2940    

DOI:10.1002/cber.19951281010

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY