Coordination Copolymerization of Severely Encumbered Isoalkenes with Ethylene:  Enhanced Enchainment Mediated by Binuclear Catalysts and Cocatalysts

This contribution describes the implementation of the binuclear organotitanium "constrained geometry catalysts" (CGCs), (mu-CH(2)CH(2)-3,3'){(eta(5)-indenyl)[1-Me(2)Si((t)()BuN)](TiMe(2))}(2)[EBICGC(TiMe(2))(2); Ti(2)] and (mu-CH(2)-3,3'){(eta(5)-indenyl)[1-Me(2)Si((t)BuN)](TiMe(2))}(2)[MBICGC(TiMe(2))(2); C1-Ti(2)], in combination with the bifunctional bisborane activator 1,4-(C(6)F(5))(2)BC(6)F(4)B(C(6)F(5))(2) (BN(2)) in ethylene + olefin copolymerization processes. Specifically examined are the classically poorly responsive 1,1-disubstituted comonomers, methylenecyclopentane (C), methylenecyclohexane (D), 1,1,2-trisubstituted 2-methyl-2-butene (E), and isobutene (F). For the first three comonomers, this represents the first report of their incorporation into a polyethylene backbone via a coordination polymerization process. C and D are incorporated via a ring-unopened pathway, and E is incorporated via a novel pathway involving 2-methyl-1-butene enchainment in the copolymer backbone. In ethylene copolymerization, Ti(2) + BN(2) enchains approximately 2.5 times more C, approximately 2.5 times more D, and approximately 2.3 times more E than the mononuclear catalyst analogue [1-Me(2)Si(3-ethylindenyl)((t)BuN)]TiMe(2) (Ti(1)) + B(C(6)F(5))(3) (BN) under identical polymerization conditions. Polar solvents are found to weaken the catalyst-cocatalyst ion pairing, thus influencing the comonomer enchainment selectivity.