Bifunctional nickel precatalysts of amido-functionalized N-heterocyclic carbenes for base-free Michael reaction under ambient conditions

A series of new bifunctional nickel precatalysts, [1-(R)-3-N-(benzylacetamido)imidazol-2-ylidene](2) Ni [R Me (1b), i-Pr (2b), and CH2Ph (3b)], containing a Lewis acidic metal site and a Lewis basic amido-N site in a pendent ligand sidearm, have been successfully designed for base-free Michael addition reaction. Specifically, the nickel (1-3)b complexes catalyzed the highly desired base-free Michael addition reactions of representative cyclic 5-membered beta-dicarbonyl and beta-ketoester substrates with a variety of activated olefinic compounds in air at ambient temperature in good to excellent yield. The nickel (1-3) b complexes were synthesized from the reactions of the corresponding imidazolium chloride salts, (1-3) a, with NiCl2 center dot 6H(2)O in presence of K2CO3 as a base in 55-73% yield. The density functional theory (DFT) studies performed on the nickel complexes suggested the presence of a strong Ni-NHC sigma-interaction in these complexes. (C) 2011 Elsevier B.V. All rights reserved