Cationic Zirconocene Hydrides:  A New Type of Highly Effective Initiators for Carbocationic Polymerizations

The reaction of [CPh 3 ][B(C 6 F 4 R) 4 ] with [Cp‘ 2 ZrH 2 ] 2 (Cp‘ = C 5 H 4 SiMe 3 ) gives the new binuclear hydrido complexes [Cp‘ 4 Zr 2 H 3 ][B(C 6 F 4 R) 4 ] (R = F, SiPr i 3 ), which are highly active initiators for the polymerization of isobutene and isobutene−isoprene copolymerizations at near-zero concentrations of ionizing solvents. The structure of the trinuclear hydride [Cp‘ 5 (η 1:η 5 -C 5 H 3 SiMe 3 )Zr 3 H 4 ] + [B(C 6 F 4 SiPr i 3 ) 4 ] - is reported.