TORSIONAL ISOMERISM OF BENT METALLOCENE COMPLEXES - THE STRUCTURES OF MESO-BIS(1-CYCLOHEXYLTETRAHYDOINDENYL)ZIRCONIUM AND RAC-BIS(1-CYCLOHEXYLTETRAHYDROINDENYL)ZIRCONIUM DICHLORIDE IN THE SOLID-STATE

Two molar equivalents of 1-cyclohexylindenyllithium were treated with ZrCl4(thf)2 to give a ca. 1:1 mixture of meso- and rac-bis(1-cyclohexylindenyl)ZrCl2 (meso-/rac-4). Catalytic hydrogenation yielded a corresponding mixture of the bis(1-cyclohexyl-4,5,6,7-trtrahydroindenyl)ZrCl2 diastereoisomers meso-5 and rac-5. In both cases the diastereomers were separated by fractional crystallization. Complexes meso- and rac-5 were characterized by an X-ray crystal structure study. In the crystal the molecular structure of complex rac-5 is C2-symmetric, with the annulated six-membered ring systems arranged towards the open front side of the bent metallocene wedge and the cyclohexyl substituents oriented anti-periplanarly in the lateral sectors. In contrast complex meso-5 has only one of the cyclohexyltetrahydroindenyl ligands arranged in this way, the cyclohexyl substituent of the other one pointing towards a central front position and the annulated six-membered ring being situated in the lateral position (C1-symmetry).