Ring-closing metathesis of sterically congested functionalized zirconocenes–ethenepolymerizationcatalysts derived from related bridged and open metallocenes

Abstract

Condensation of allylcyclopentadiene 1 with acetone in the presence of pyrrolidine gave 2-allyl-6,6-dimethylfulvene (2). Methyllithium addition gave lithium 1-allyl-3-tert-butylcyclopentadienide (3). Transmetallation with 0.5 equiv. of ZrCl₄ yielded the respective functionalized zirconocene dichloride complexes meso-4 and rac-4, which were both isolated isomerically pure. With 10 mol% of [Cl₂(PCy₃)₂RuCHPh] the rac-4 diastereoisomer underwent a clean intramolecular ring-closing olefin metathesis reaction to yield the ansa-zirconocene complex rac-6. The complexes meso-4, rac-4 and rac-6 were characterized by X-ray diffraction. Treatment of the open metallocenes meso-4 and rac-4, respectively, with excess methylalumoxane gave rather active ethene polymerization catalysts. The corresponding catalyst derived from the conformationally restricted bulky ansa-metallocene rac-6 is markedly less active.