Preparation, Structure, and Olefin Polymerization Behavior of Functionalized Nickel(II) N-Heterocyclic Carbene Complexes^†

Picolyl-functionalized N-heterocyclic carbene complexes have been synthesized by a route involving carbene transfer from Ag(I) carbene precursors. The Ag complexes undergo facile reaction with Ni(PPh3)2Cl2 to yield the carbene complexes Ni(C∧N)2Cl2 (C∧N = 3-methyl-1-picolylimidazolin-2-ylidene (2a), 3-benzyl-1-picolylimidazolin-2-ylidene (2b)). Complexes 2a,b have been characterized by IR and 1H and 13C NMR spectra and elemental analyses. The molecular structures of complexes 2a,b have been confirmed by X-ray single-crystal analyses. The carbene complex 2a shows high catalytic activities of up to 2.6 × 107 g of PNB (mol of Ni)-1 h-1 for the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst and exhibits moderate catalytic activity (3.3 × 105 g of PE (mol of Ni)-1 h-1) for ethylene polymerization. Catalytic activities, polymer yield, molecular weights, and molecular weight distributions of polynorbornene have been investigated under the various reaction conditions.