RING-OPENING ZIEGLER POLYMERIZATION OF METHYLENECYCLOALKANES CATALYZED BY HIGHLY ELECTROPHILIC D(0) F(N) METALLOCENES - REACTIVITY, SCOPE, REACTION-MECHANISM, AND ROUTES TO FUNCTIONALIZED POLYOLEFINS/

A series of zirconium and lanthanide metallocene catalysts are active in the regioselective ring-opening polymerization of strained exo-meth ylenecycloalkanes to yield exo-methylene-functionalized polyethylenes. MCB (methylenecyclobutane) affords the polymer [CH2CH2CH2C(CH2)](n) u nder the catalytic action of (1,2-Me(2)Cp)(2)ZrMe(+)-MeB(C6F5)(3)(-), and MCP (methylenecyclopropane) affords the polymer [CH2CH2C(CH)(2)](n ) under the catalytic action of [(Me(5)Cp)(2)LuH](2). Reversible deact ivation of the [(Me(5)Cp)(2)LuH](2) catalyst is observed in the MCP po lymerization reaction and is ascribed to formation of a Lu-allyl speci es based on D2O quenching experiments. In contrast, the catalysts [Me( 5)Cp)(2)SmH](2) and [(Me(5)Cp)(2)LaH](2) yield the dimer 1,2-dimethyle ne-3-methylcyclopentane (DMP) from MCP with high chemoselectivity. The mechanism of dimerization is proposed to involve the intermediacy of 3-methylene-1,6-heptadiene (MHD) and is supported by the observation t hat independently synthesized MHD is smoothly converted to DMP under c atalytic conditions. (Me(5)Cp)(2)ZrMe(+)MeB(C6F5)(3)(-) catalyzes the polymerization of MCP to a polyspirane consisting of 1,3-interlocked f ive-membered rings (poly(1,4:2,2:butanetetrayl), (C4H6)(n)). From end group analysis, the reaction pathway is proposed to consist of beta-al kyl shift-based ring-opening followed by an intramolecular insertive, ring-closing ''zipping-up'' process. AM1-level computations indicate t hat the zipping-up reaction is exothermic by similar to 16 kcal/(mol o f ring closure). Under the same catalytic conditions, the monomers met hylenecyclopentane, methylenecyclohexane, and 2-methylenenorbornane un dergo double bond migration (to the adjacent internal position) rather than polymerization. In contrast to the relatively restrictive requir ements for homopolymerization, MCB-ethylene copolymerization is cataly zed by a wide variety of zirconocenium catalysts, including those gene rated conveniently From MAO, to afford high molecular weight {[CH2CH2] (x)[CH2CH2CH2C-(CH2)](y)}(n) copolymers with the incorporated MCB havi ng an exclusively ring-opened microstructure. The activity of the cata lysts in incorporating MCB into the polymer chain follows the order: C p(2)ZrMe(+) > (1,2-Me(2)Cp)(2)ZrMe(+) much greater than (Me(5)Cp)(2)Zr Me(+), regardless of the counteranion identity. Labeling experiments w ith (CH2)-C-13=(CH2)-C-13 confirm that MCB ring-opening occurs with C2 -C3, C2-C5 bond scission. MCP-ethyIene copolymerization to yield high molecular weight {[CH2CH2](x)[CH2CH2C(CH2)](y)} having an exclusively ring-opened microstructure is catalyzed by [(Me(5)Cp)(2)LuH](2) and [( Me(5)Cp)(2)SmH](2). When [(Me(5)Cp)(2)LaH](2) is used as the catalyst, more than 50% of the MCP is located at the chain ends in a dienyl str ucture. The only zirconium polymerization catalyst which incorporates MCP in the ring-opened form in a moderate percentage is [(Me(4)CpSiMe( 2)(N(t)Bu)]ZrMe(+) B(C6F5)(4)(-). The activity of d(0)/f(0) catalysts in incorporating MCP into the polymer follows the order: [(Me(4)CpSiMe (2)(N(t)Bu)]ZrMe(+)B(C6F5)(4)(-) >[(Me(5)Cp)(2)LuH](2) > [(Me(5)Cp)(2) SmH](2) > [(Me(5)Cp)(2)LaH](2).