ansa-metallocene derivatives : XVI. Chiral titanocene and zirconocene derivatives with symmetrically substituted, tetramethylethanediyl-bridged ligand frameworks. Crystal structures of representative examples

Abstract

Syntheses of disubstituted, tetramethylethanediyl-bridged titanocene derivatives (CH₃)₄C₂(1-C₅H₃-3-R)₂TiCl₂, with R  t-butyl, trimethylsilyl, isopropyl, α,α-dimethylbenzyl and 1-phenylcyclohexyl, by reductive coupling of the appropriately substituted 6,6-dimethylpentafulvenes with Mg/CCl₄ and reaction of the resulting di-Grignard compounds with TiCl₃·3THF are described along with those of several zirconium analogues. The reaction sequence in each case gives, together with the desired racemate, comparable amounts of the corresponding meso-configurated complex. The NMR data for the racemic and meso diastereomers of these compounds and crystal structures of one meso and several racemic representatives are reported.