The group 4 ansa-metallocene complexes with chiral substituent bearing cyclopentadienyl ligands, [M{Me2Si(eta(5)-C5Me4)(eta(5)-C5H3{CHRR'})}Cl-2] (R=Pr-i,R'=Me(9); R=Pr-i, R'=Ph (10); R=Bu, R'=Me(11); R=Bu',R'=Ph(12); M=Zr(a), Hf (b)), were synthesized by the reaction of the dilithium compounds, Li-2{Me2Si(C5Me4)(C5H3{CHRR'})} (R=Pr-i, R'=Me (5); R=Pr-i, R'=Ph (6); R=Bu', R'=Me (7); R = Bu', R'= Ph (8)), with the tetrachloride salts of the transition metal. The molecular structures of 1 la and 12a have been determined by single-crystal X-ray diffraction studies. The catalytic behaviour of 9-12 in the polymerization of ethylene and propylene has been studied. Isotactic polypropylene with [mmmm] pentads of the order of 60% were obtained with the C, symmetric ansa-zirconocene catalysts. (c) 2006 Elsevier B.V. All rights reserved.