Combined Experimental and Computational Investigation of the Mechanism of Nickel-Catalyzed Three-Component Addition Processes

The mechanism of nickel-catalyzed couplings of an enone, alkyne, and organozinc has been studied. Adducts of the substrates with nickel(0) have been isolated and characterized, and their reactivity was examined. A potential intermediate was demonstrated to not be kinetically competent in catalytic cyclizations. A computational approach employing the B3LYP density functional method and the 6-31G(d) basis set was used to examine mechanistic possibilities that were consistent with experimental observations, and a modified mechanism for the catalytic cyclizations was formulated. The newly proposed mechanism involves production of an active catalyst that involves a novel interaction between Ni(0) and dimethylzinc.