The ansa-indene ligands {1-Me2Si(3-C9H6R)2} [R = Me (1), nPr (2), nBu (3), and Bz (4)] were prepared by alkylation of the unsubstituted ansa-indene. These ligands were converted, by reaction with nBuLi, to the di-lithium compounds [Li2{1-Me2Si(3-C9H5R)2}] [R = Me (5), nPr (6), nBu (7), and Bz (8)]. ansa-Zirconocenes, [Zr{1-Me2Si(3-η5-C9H5R)2}Cl2] [R = Me (9), nPr (10), nBu (11), and Bz (12)], have been prepared by the reaction of ZrCl4 with 5–8 in diethyl ether/toluene at–78 °C. The molecular structure of meso-[Zr{1-Me2Si[3-η5-C9H5(CH3)]2}Cl2] (9) and rac-[Zr{1-Me2Si[3-η5-C9H5(CH2CH2CH3)]2}Cl2] (10) have been determined by single-crystal X-ray diffraction studies. Ethylene polymerization catalysis has been studied for complexes 9–12 as a mixture of meso and rac isomers in the presence of methylaluminoxane (MAO) as cocatalyst. Complexes 9–12 exhibit high activities and give rise to polyethylene with low molecular weights without the introduction of molecular hydrogen. In addition, active species from these complexes were found to be very stable in comparison with unsubstituted analogues.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)