CATIONIC GROUP-IV METAL ALKYL COMPLEXES AND THEIR ROLE AS OLEFIN POLYMERIZATION CATALYSTS - THE FORMATION OF ETHYL-BRIDGED DINUCLEAR AND HETERODINUCLEAR ZIRCONIUM AND HAFNIUM COMPLEXES

Bis(cyclopentadienyl)hafnium diethyl (1) reacts with [CPh(3)][B(C6F5)(4)] in dichloromethane at -60 degrees C with hydride rather than alkyl transfer to give triphenylmethane and the ethyl-bridged dinuclear complex [(Cp(2)HfEt)(2)(mu-Et)][B(C6F5)(4)] (2). The complex is less stable than analogous methyl complexes but is stabilized by the presence of excess Cp(2)HfEt(2). The reaction between Cp(2)HfEt(2), [CPh(3)l[B(C6F5)(4)], and AlEt(3) under analogous conditions leads to [Cp(2)Hf(mu-Et)(2)AlEt(2)][B(C6F5)(4)] (3). The reaction between Cp(2)HfMe(2) and AlEt(3) leads to alkyl ligand exchange to give, successively, Cp(2)Hf(Me)(Et) and Cp(2)HfEt(2). Similar fast ligand exchange reactions take place between Cp'(2)ZrMe(2) and AlEt(3) and can be used for generating the thermally labile complex Cp'(2)ZrEt(2) as a precursor for cationic polymerization catalysts [Cp'(2) = Cp(2) rac-Me(2)Si(Ind)(2)]. Polymerization activities of rac-[Me(2)Si(Ind)(2)Zr(mu-R)(2)AIR(2)I[B(C6F5)(4)] increase in the order R = Me < Et.