SYNTHESES, STRUCTURES AND REACTIONS OF SOME NEW BENZYL-SUBSTITUTED CYCLOPENTADIENYL TITANIUM COMPLEXES

Twenty eight new benzyl-substituted cyclopentadienyl titanium complexe s have been synthesized. Among them, five typical molecular structures have been studied by X-ray analysis. It was found that in the prepara tion of ortho-MeO-containing benzyl-substituted titanium complexes, wh en 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 t emperature is favourable to the cyclization. At 80 degrees C, the norm al ortho-MeO benzyl-substituted cyclopentadienyl titanium complex 26 m ay be spontaneously converted into metallocyclic complex 19. The posit ion of the MeO group on the benzene ring is the key factor to the cycl ization. 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 pr oposed. (C) 1997 Elsevier Science S.A.