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

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