Tin-bridged ansa-metallocenes of zirconium: Synthesis and catalytic performance in olefin polymerization

The first tin-bridged zirconocenes [(CH3)(2)Sn(C5H4)(2)]Zr[N(CH3)(2)](2) (3) and Sn((C5H4)(2)Zr[N(CH3)(2)](2)}(2) (4) have been obtained from tetrakis(dimethylamido)zirconium (1) and the CH-acidic ligands (CH3)(2)Sn(C5H5)(2) (2a) and Sn(C5H5)(4) (2b), respectivily. The ansa-zirconocene 3 is formed in quantitative yield, 4 in 81% yield. The bi- and trimetallic complexes 3(ZrSn) and 4(Zr2Sn) polymerize ethylene more efficiently than the well-known silicon-bridged analogue of 3 (Si instead of Sn).