Synthesis of a series of new, highly electrophilic, monocyclopentadienyltitanium olefin polymerization initiators 

Abstract

The new compounds Ti(η-C₅Me₅)Me₂E (E = C₆F₅ or OC₆F₅) and Ti(η-C₅Me₅)Me(OC₆F₅) ₂ have been synthesized and characterized by a variety of techniques, including ^47/49Ti NMR spectroscopy. All three compounds react with the borane B(C₆F₅)₃ to form the highly electrophilic but thermally unstable species Ti(η-C₅Me₅)Me(E)(µ-Me)B(C₆F ₅)₃ and [(η-C₅Me₅)Ti(OC₆F₅) ₂][BMe(C₆F₅)₃], the solution structures and dynamics of which are investigated and compared with those of the known compound Ti(η-C₅Me₅)Me₂(µ-Me)B(C₆ F₅)₃. Interestingly, Ti(η-C₅Me₅)Me(C₆F₅)( µ-Me)B(C₆F₅)₃ undergoes neither significant ion-pair dissociation to the solvent separated ions [(η-C₅Me₅)TiMe(C₆F₅)] ⁺ and [BMe(C₆F₅)₃]^- nor borane dissociation to its precursors (η-C₅Me₅)TiMe₂(C₆F ₅) and B(C₆F₅)₃; indeed, both rotation about the Ti–C₆F₅ bond and inversion at the chiral metal are slow on the NMR time-scale. In contrast, Ti(η-C₅Me₅)Me(OC₆F₅)( µ-Me)B(C₆F₅)₃ is more labile and, like Ti(η-C₅Me₅)Me₂(µ-Me)B(C₆ F₅)₃, undergoes ion-pair dissociation, while [(η-C₅Me₅)Ti(OC₆F₅) ₂][BMe(C₆F₅)₃] exists in solution as the solvent separated ion species [(η-C₅Me₅)Ti(OC₆F₅) ₂]⁺ and [BMe(C₆F₅)₃]^- in equilibrium with its precursors, (η-C₅Me₅)TiMe(OC₆F₅) ₂ and B(C₆F₅)₃.

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