Synthesis of bis(tert-butyl)cyclopentadienyl derivatives of titanium and zirconium. NMR spectra and dynamic behavior of the base-free [Zr(1,3-tBu2-µ5-C5H3)(CH2Ph)2]+ cation

Reaction of Si(1,3-tBu2-C5H3)Me3 with MCl4 (M = Ti, Zr) in toluene or hexane at room temp. affords the new trichloromonociclopentadienyl-type derivs. [M(1,3-tBu2-η5-C5H3)Cl3] [M = Ti (2), Zr (3)]. Treatment of complexes 2 and 3 with appropriate alkylating reagents in hexane gives the 1,3-di(tert-butyl)cyclopentadienyl trialkyl titanium and zirconium complexes [M(1,3-tBu2-η5-C5H3)R3] [M = Ti, R = CH3, CH2Ph; M = Zr, R = CH3, CH2Ph (7), CH2CMe2Ph]. Interestingly, when 2 reacts with 3.1 equiv of LiCH2CMe2Ph in hexane at room temp. the ring-tert-butyl-metalated complex [Ti(1-tBu-3-CMe2CH2-η5-C5H3) (CH2CMe2Ph)2] was isolated in 90% yield. The cationic mono(1,3-di-(tert-butyl)cyclopentadienyl) dibenzyl zirconium species [Zr(1,3-tBu2-η5-C5H3)(CH2Ph)2]+, generated in situ by reaction of the tribenzyl complex 7 with B(C6F5)3 or [CPh3]+[B(C6F5)4]- reagents, is reported and their dynamic NMR behavior in CD2Cl2 solns. at low temps. is studied.Financial support for this research by DGICYT (Project\ud PB92-0178-C) is gratefully acknowledged. J.I.A.\ud acknowledges Repsol Petróleo S.A. for a fellowship