Titanium “constrained geometry” complexes with pendant arene groups

Abstract

The synthesis of the proligands C₅Me₄HSiMe₂N(H)R) (R = CMe₂Ph 1, 2-C₆H₄Ph 2) was accomplished via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe₂(C₅Me₅H). Generation of the dilithio salt and reaction with TiCl₃·(THF)₃ followed by oxidation gave C₅Me₄SiMe₂N(C₆H₄Ph)TiCl₂ (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with (Me₂N)₂TiCl₂ afforded C₅Me₄(SiMe₂NR)Ti(NMe₂)₂ (R = CMe₂Ph 4, 2-C₆H₄Ph 5), respectively, in good yields Treatment with MeI gave the analogs C₅Me₄(SiMe₂NR)TiI₂ (R = CMe₂Ph 6, 2-C₆H₄Ph 7). Reduction of 7 with potassium graphite afforded C₅Me₄(SiMe₂NC₆H₄Ph)Ti 8. Treatment of 6 and 7 with MeMgBr afforded C₅Me₄(SiMe₂NR)TiMe₂ (R = CMe₂Ph 9, 2-C₆H₄Ph 10). Complexes 9 and 10 in combination with the activator [Ph₃C][B(C₆F₅)₄] catalyzed the polymerization of styrene and ethylene. Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity, compound 9 showed markedly higher activity than 10 and (C₅Me₄)SiMe₂(NtBu)]TiMe₂.