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

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Abstract
This contribution describes the implementation of the binuclear organotitanium “constrained geometry catalysts” (CGCs), (μ-CH2CH2-3,3‘){(η5-indenyl)[1-Me2Si(tBuN)](TiMe2)}2[EBICGC(TiMe2)2; Ti 2] and (μ-CH2-3,3‘){(η5-indenyl)[1-Me2Si(tBuN)](TiMe2)}2[MBICGC(TiMe2)2; C1 − Ti 2], in combination with the bifunctional bisborane activator 1,4-(C6F5)2BC6F4B(C6F5)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 ∼2.5 times more C, ∼2.5 times more D, and ∼2.3 times more E than the mononuclear catalyst analogue [1-Me2Si(3-ethylindenyl)(tBuN)]TiMe2 (Ti 1) + B(C6F5)3 (BN) under identical polymerization conditions. Polar solvents are found to weaken the catalyst−cocatalyst ion pairing, thus influencing the comonomer enchainment selectivity.

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