Abstract The zirconocene complexes [Zr(η 5 ‐C 5 H 5 ){η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH=CH 2 )}Cl 2 ] ( 4 ) and [Zr{η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH=CH 2 )} 2 Cl 2 ] ( 5 ) were synthesised from the reaction of the lithium derivative [Li{C 5 H 4 (CMe 2 CH 2 CH 2 CH=CH 2 )}] ( 1 ) with [Zr(η 5 ‐C 5 H 5 )Cl 3 ] or ZrCl 4 , respectively. The ansa ‐zirconocene complex [Zr{Me 2 Si(η 5 ‐C 5 Me 4 )(η 5 ‐C 5 H 3 {CMe 2 CH 2 CH 2 CH=CH 2 })}Cl 2 ] ( 6 ) was obtained from the reaction of the lithium precursor [Li 2 {Me 2 Si(η 5 ‐C 5 Me 4 )(η 5 ‐C 5 H 3 {CMe 2 CH 2 CH 2 CH=CH 2 })}] ( 3 ) with zirconium tetrachloride. Catalytic hydrogenation of 4 – 6 gave the zirconocene complexes [Zr(η 5 ‐C 5 H 5 ){η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH 2 CH 3 )}Cl 2 ] ( 7 ), [Zr{η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH 2 CH 3 )} 2 Cl 2 ] ( 8 ) and [Zr{Me 2 Si(η 5 ‐C 5 Me 4 )(η 5 ‐C 5 H 3 {CMe 2 CH 2 CH 2 CH 2 CH 3 })}Cl 2 ] ( 9 ), respectively. Hydroboration of 4 – 6 with 9‐BBN (9‐borabicyclo[3.3.1]nonane) yielded [Zr(η 5 ‐C 5 H 5 ){η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH 2 CH 2 BC 8 H 14 )}Cl 2 ] ( 10 ), [Zr{η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH 2 CH 2 BC 8 H 14 )} 2 Cl 2 ] ( 11 ) and[Zr{Me 2 Si(η 5 ‐C 5 Me 4 )(η 5 ‐C 5 H 3 {CMe 2 CH 2 CH 2 CH 2 CH 2 BC 8 H 14 })}Cl 2 ] ( 12 ), respectively, and the catalytic hydrosilylation of 4 – 6 with SiHMe 2 Cl gave [Zr(η 5 ‐C 5 H 5 ){η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH 2 CH 2 SiMe 2 Cl)}Cl 2 ] ( 13 ), [Zr{η 5 ‐C 5 H 4 (CMe 2 CH 2 CH 2 CH 2 CH 2 SiMe 2 Cl)} 2 Cl 2 ] ( 14 ) and [Zr{Me 2 Si(η 5 ‐C 5 Me 4 )(η 5 ‐C 5 H 3 {CMe 2 CH 2 CH 2 CH 2 CH 2 SiMe 2 Cl})}Cl 2 ] ( 15 ), respectively. The dinuclear complex [Cl 2 Zr{Me 2 Si(η 5 ‐C 5 Me 4 )(η 5 ‐C 5 H 3 {CMe 2 (CH 2 ) 4 SiMe 2 OSiMe 2 (CH 2 ) 4 Me 2 C}η 5 ‐C 5 H 3 )(η 5 ‐C 5 Me 4 )SiMe 2 }ZrCl 2 ] ( 16 ) was obtained upon controlled hydrolysis of 15 . The zirconocene compounds were tested as catalysts in the polymerisation of ethylene and propylene. Isotactic polypropylene with [mmmm] pentads of the order of 75 % were obtained with the ansa ‐zirconocene catalysts, whereas the unbridged metallocene catalysts produced atactic polypropylene. The molecular structures of 4 and 5 were determined by single‐crystal X‐ray diffraction studies.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)