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

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Abstract
The new compounds Ti(η-C 5 Me 5 )Me 2 E (E = C 6 F 5 or OC 6 F 5 ) and Ti(η-C 5 Me 5 )Me(OC 6 F 5 ) 2 have been synthesized and characterized by a variety of techniques, including 47/49 Ti NMR spectroscopy. All three compounds react with the borane B(C 6 F 5 ) 3 to form the highly electrophilic but thermally unstable species Ti(η-C 5 Me 5 )Me(E)(µ-Me)B(C 6 F 5 ) 3 and [(η-C 5 Me 5 )Ti(OC 6 F 5 ) 2 ][BMe(C 6 F 5 ) 3 ], the solution structures and dynamics of which are investigated and compared with those of the known compound Ti(η-C 5 Me 5 )Me 2 (µ-Me)B(C 6 F 5 ) 3 . Interestingly, Ti(η-C 5 Me 5 )Me(C 6 F 5 )( µ-Me)B(C 6 F 5 ) 3 undergoes neither significant ion-pair dissociation to the solvent separated ions [(η-C 5 Me 5 )TiMe(C 6 F 5 )] + and [BMe(C 6 F 5 ) 3 ] - nor borane dissociation to its precursors (η-C 5 Me 5 )TiMe 2 (C 6 F 5 ) and B(C 6 F 5 ) 3 ; indeed, both rotation about the Ti–C 6 F 5 bond and inversion at the chiral metal are slow on the NMR time-scale. In contrast, Ti(η-C 5 Me 5 )Me(OC 6 F 5 )( µ-Me)B(C 6 F 5 ) 3 is more labile and, like Ti(η-C 5 Me 5 )Me 2 (µ-Me)B(C 6 F 5 ) 3 , undergoes ion-pair dissociation, while [(η-C 5 Me 5 )Ti(OC 6 F 5 ) 2 ][BMe(C 6 F 5 ) 3 ] exists in solution as the solvent separated ion species [(η-C 5 Me 5 )Ti(OC 6 F 5 ) 2 ] + and [BMe(C 6 F 5 ) 3 ] - in equilibrium with its precursors, (η-C 5 Me 5 )TiMe(OC 6 F 5 ) 2 and B(C 6 F 5 ) 3 .

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