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)(2)Cl-2 to yield the carbene complexes Ni(Cboolean ANDN)(2)Cl-2 (Cboolean ANDN = 3-methyl-1-picolylimidazolin-2-ylidene (2a), 3-benzyl-1-picolylimidazolin-2-ylidene (2b)). Complexes 2a,b have been characterized by IR and H-1 and C-13 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 x 10(7) 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 x 10(5) 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.