HETEROBIMETALLIC SIGMA,PI-ACETYLIDE-BRIDGED COMPLEXES FROM DISUBSTITUTED 1,3-BUTADIYNES

It has been shown that a nickel(0) complex of bis(trimethylsilyl)butadiyne, (Ph(3)P)(2)Ni(eta(2)Me(3)SiC=CC=CSiMe(3)), readily reacts with the titanocene Cp(2)Ti(Me(3)SiC=CSiMe(3)) and zirconocene Cp(2)Zr(THF)(Me(3)SiC=CSiMe(3)) complexes to form the heterobimetallic, doubly acetylide bridged complexes Cp(2)M(mu-eta(1):eta(2)-C=CSiMe(3))Ni(PPh(3))(mu-eta(1);eta(2)-C=CSiMe(3)) (M = Ti (1), M = Zr (2)). The structures of these complexes have been established by X-ray crystal structure analysis. Two sigma,pi-bridging acetylide units are sigma-bonded to different metals and pi-bonded to the second metal. Compound 1 in solution at 303 K is highly fluxional. An NMR study showed that at 190 K an equilibrium exists between one isomer with two nonequivalent and another isomer with two equivalent acetylide units. The cleavage of the central C-C single bond of the butadiyne was not observed in the reaction of the unsymmetrically substituted butadiyne PhC=CC=CSiMe(3) with titanocene ''Cp(2)Ti'' generator Cp(2)Ti(Me(3)SiC=CSiMe(3)). The product is a bridging tetradehydro-(1-3-eta):(2-4-eta)-trans,trans-butadiene unit (zigzag butadiyne) between two titanium centers in Cp(2)Ti{mu-(1-3-eta):(2-4-eta)-trans,trans-PhC=CC=CSiMe(3)}TiCp(2) (5). If the phenyl(trimethylsilyl)butadiyne is complexed by nickel(0), the reaction with the titanocene generated from Cp(2)Ti(Me(3)SiC=CSiMe(3)) yields the heterobimetallic complex Cp(2)Ti(mu-eta(1):eta(2)-C=CSiMe(3))(mu-eta(1):eta(2)-C=CPh)Ni(PPh(3)) (6). Both acetylide units are sigma-bonded to the titanium atom and pi-bonded to the nickel atom, giving a ''tweezerlike'' structure.