Syntheses, structures and reactions of some new benzyl-substituted cyclopentadienyl titanium complexes

Abstract

Twenty eight new benzyl-substituted cyclopentadienyl titanium complexes have been synthesized. Among them, five typical molecular structures have been studied by X-ray analysis. It was found that in the preparation of ortho-MeO-containing benzyl-substituted titanium complexes, when both two substituents on benzylic carbon atom are Et or more large group, titanoxacycle complexes are always formed. The cyclization was promoted by the presence of halides. The activity order of halides for the cyclization is: LiI-NaI > LiBr-Br 2 > NaBr-KI > KBr > I 2. High temperature is favourable to the cyclization. At 80°C, the normal ortho-MeO benzyl-substituted cyclopentadienyl titanium complex 26 may be spontaneously converted into metallocyclic complex 19. The position of the MeO group on the benzene ring is the key factor to the cyclization. In the case of meta- and para-MeO benzyl-substituted titanium complexes 23 and 25, there was no possibility to form a titanoxacycle complex, such as 19, because the MeO group is too far from titanium. A probable mechanism involving a four-membered transition state was proposed.