SYNTHESIS OF BASE-FREE CATIONIC ZIRCONIUM METHYL AND BENZYL COMPLEXES - THE CRYSTAL AND MOLECULAR-STRUCTURE OF (C5H3(SIME3)2-1,3)2ZRME(MU-ME)B(C6F5)3

The reaction of the dimethyl complexes rac-Me2Si(Ind)2ZrMe2 (1a) (Ind = eta5-indenyl) and {C5H3(SiMe3)2-1,3}2ZrMe2 (2a) with B(C6F5)3 gives the zwitterionic compounds rac-Me2Si(Ind)2Zr-(Me)(mu-Me)B(C6F5)3 (1b) and {C5H3(SiMe3)2-1,3}2ZrMe(mu-Me)B(C6F5)3 (2b), respectively. The crystal structure of 2b has been determined. The compound possesses a bridging methyl group with a long zirconium-carbon distance of 2.667 (5) angstrom and an almost linear Zr-C-B arrangement [bond angle 170.5(3)-degrees]. Two of the bridging methyl hydrogens show close Zr-H contacts of 2.47(3) and 2.44(3) angstrom. In contrast to the zwitterionic structure of 2b, the reaction of B(C6F5)3 with the dibenzyl complexes CP'2Zr(CH2Ph)2 [CP'2 = rac-Me2Si(Ind)2 (1C), {C5H3(SiMe3)2-1,3}2 (2c), (C5H5)2 (3c), rac-C2H4(Ind)2 (4c), Me2C(C5H4)(Flu) (5c)] in dichloromethane at -50-degrees-C leads to the ionic compounds [CP'2Zr(CH2Ph)]+[PhCH2B(C6F5)3]- (1d-5d) which contain eta2-coordinated benzyl ligands and noncoordinated [PhCH2B(C6F5)3]-counteranions. The complexes are thermally unstable in dichloromethane solution but stable in hydrocarbons. Complexes with bridging benzyl ligands are not observed. In the case of the hydrocarbon-soluble complex [{C5H3(SiMe3)2-1,3}2Zr(eta2-CH2Ph)]+[PhCH2B(C6F5)3]- (2d) it is shown that the ionic structure is maintained in toluene-d8 solution at 60-degrees-C, i.e. under polymerization conditions. By contrast, the mono(cyclopentadienyl) complex CpZr(CH2Ph)3 reacts with B(C6F5)3 to give CpZr(eta2-CH2-Ph)2(eta6-PhCH2B(C6F5)3 (7), where the phenyl ring of the anion is pi-coordinated to the metal. The reaction of 1c with [CPh3][B(C6F5)4] gives the related complex [Me2Si(Ind)2Zr(eta2-CH2-Ph)][B(C6F5)4] (1e). The complexes are highly active catalysts for the polymerization of ethene and propene.