Synthesis of pure racemic isomers of ansa-titanocene dichlorides: conformational preferences are determined by substitution patterns on the cyclopentadienyl rings

A series of [1,2-ethylene-1,1'-bis(4-alkyl-2-methylcyclopentadienyl)] titanium dichlorides (3a-c) have been prepared by a new route wherein the presence of the 2-methyl substituent on the cyclopentadiene rings enables the stereoselective preparation of racemic isomers. Racemic ethylene-1,1'-bis(2-methyl-4-tert-butylcyclopentadienyl) titanium dichloride (3c) was characterized by an X-ray structural determination