Homogeneous α-Olefin Polymerizations over Racemic Ethylene-Bridged ansa-Bis(2-(tert-butyldimethylsiloxy)- 1-indenyl) and ansa-Bis(2-(tert-butyldimethylsiloxy)- 4,5,6,7-tetrahydro-1-indenyl) Metallocene Dichlorides

Ethylene and propylene were polymerized over the siloxy-substituted bis(indenyl) ansa -metallocenes, rac -[ethylenebis(2-( tert -butyldimethylsiloxy)indenyl)]zirconium dichloride ( 1 ), rac -[ethylenebis(2-( tert -butyldimethylsiloxy)-4,5,6,7-tetrahydroindenyl)]zirconium dichloride ( 2 ), and rac -[ethylenebis(2-( tert -butyldimethylsiloxy)indenyl)]hafnium dichloride ( 3 ), using methylaluminoxane (MAO) and trityl tetrakis(pentafluorophenyl)borate as cocatalysts. Especially complex 1 forms a highly active catalyst precursor for the polymerization of α-olefins. Synthesis and characterization of 2 and 3 are described. The 1 /MAO and 3 /MAO catalyst systems show high polymerization activities at exceptionally low [Al]:[Zr] ratios [(100−250):1]. For both catalysts, extensive chain transfer to aluminum is observed as the predominant chain-transfer mechanism. Preliminary results from copolymerization of ethylene with 1-hexene and 1-hexadecene over 1 /MAO indicate a good comonomer response.