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|Title:||Nickel Complexes of N/O-Functionalized N-Heterocyclic Carbenes as Precatalysts for Michael Reactions in Air at Room Temperature Under the Much Preferred Base-Free Conditions|
|Publisher:||WILEY-V C H VERLAG GMBH|
|Citation:||EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (13), 1932-1941|
|Abstract:||A series of several new nickel precatalysts supported over N/O-functionalized N-heterocychc carbenes (NHC) for the Michael reactions of beta-dicarbonyl, beta-keto ester, beta-diester, and alpha-cyano ester compounds with alpha,beta-unsaturated carbonyl compounds in air at ambient temperature under the much preferred base-free conditions are reported. Specifically, the nickel complexes, [1-(R(1)-aminocarbonylmethyl)-3-R(2)-imidazol-2-ylidene](2)Ni [R(1) = 2-C(6)H(4)(OMe); R(2) = Me (1b), iPr (2b), CH(2)Ph (3b) and R(1)= 2-CH(2)C(4)H(3)O; R(2) = Me (4b), CH(2)Ph (5b)] carried out the highly convenient base-free Michael addition of the activated C-H compounds across alpha,beta-unsaturated carbonyl compounds in air at room temperature. The complexes 1b-5b were synthesized by the direct reaction of the respective imidazohum chloride salt with NiCl(2)-6H(2)O in CH(3)CN in the presence of K(2)CO(3) as a base. The exceptional stability of 1b-5b has been attributed to the deeply buried nickel-NHC sigma-bonding molecular orbitals as evidenced from the density functional theory (DFT) studies. ((C) 2009)|
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