Abstract
Highly convenient base-free Michael reaction of beta-dicarbonyl, beta-keto ester, and alpha-cyano ester compounds with activated ethylene compounds in air at ambient temperature catalyzed by a series of new nickel complexes, 1b-4b, of N/O-functionalized N-heterocyclic carbenes (NHC) are reported. Quite interestingly, of these nickel complexes, 1b and 2b were found to be of the [(NHC)(2)Ni-OH] type bearing a terminal [Ni-OH] moiety and are among the few known structurally characterized examples of monomeric terminal [Ni-OH] complexes. Compounds 3b and 4b, on the other hand, were found to be of the commonly encountered [(NHC)(2)Ni]-type complexes. More significantly, both the [(NHC)(2)Ni-OH] -type complexes 1b and 2b and the [(NHC)(2)Ni]-type complexes 3b and 4b were synthesized using same synthetic methodology by sheer modulation of the N-substituents on the N-heterocyclic carbene ring by the reaction of the imidazolium chloride salts with NiCl2 center dot 6H(2)O in the presence of K2CO3 as a base.