CONFORMATIONAL-ANALYSIS OF NONBRIDGED BENT METALLOCENE ZIEGLER-CATALYST PRECURSORS-DETECTION OF THE 3RD TORSIONAL ISOMER

The series of (1-terpenylindenyl)(2)ZrCl2 bent metallocene complexes ( with terpenyl substituents neomenthyl, neoisomenthyl, menthyl, and iso menthyl) were obtained from the reaction of the respective 1-terpenyli ndenyl lithium reagents with ZrCl4. In each case a single racem-like d iastereoisomer was isolated pure by crystallization. The conformationa l analysis of the bent metallocene systems was carried out by variable temperature H-1 NMR spectroscopy. It has revealed the existence and e quilibration of three different bent metallocene torsional isomers. Tw o of these are C-2-symmetric and carry their bulky terpenyl substituen ts either in the lateral or the front sector of the bent metallocene w edge (descriptors bis-lateral:anti (conformer A) and bis-central:syn ( conformer B)), whereas the rotational isomer C (central, lateral:gauch e) is of lower symmetry. The (1-terpenylindenyl)(2)ZrCl2/methylalumoxa ne systems are active propene polymerization catalysts. The equilibriu m amount of the ''stereochemically productive'' C-2-symmetric bis-late ral:anti bent metallocene conformer A correlates qualitatively with th e observed isotacticity of the propene polymerization process at the r espective group 4 bent metallocene catalyst system.