Copolymerization of Ethylene with Norbornene Catalyzed by Cationic Rare-Earth Metal Half-Sandwich Complexes

We report on copolymerizations of ethylene with norbornene with half-sandwich rare-earth metal catalysts generated by activation of dialkyl complexes [Ln(eta(5)-C(5)Me(4)SiMe(2)R)(eta(1)-CH(2)SiMe(3))(2)(THF)] (Ln = Sc, R = Me (1); Ln = Sc, R = C(6)F(5) (2); Ln = Y, R = C(6)F(5) (3); Ln = Lu, R = C(6)F(5) (4)) with [Ph(3)C][B(C(6)F(5))(4)]. Complexes 1 and 2 showed excellent activities, whereas complex 3 gave poor activity and 4 was practically inactive. Weak stabilization of metal center by bulkier silyl group of the tetramethylcyclopentadienyl ring in complexes 2 and 3 allows controlled copolymerization (M(w)/M(n) < 1.3). Mainly atactic alternating P(E-co-N) copolymers were obtained with the active catalytic systems. These copolymerizations were well described by first-order Markov statistics.