DFT study on the mechanism of palladium(II)-catalyzed reaction of allyl-substituted 3,4-dienoate, alkyne and carbon monoxide

Abstract

The reaction mechanism of palladium-catalyzed allyl-substituted 3,4-dienoate, alkyne and carbon monoxide to form ynone has been theoretically investigated by using density functional theory calculations. Two reaction mechanisms have been calculated. In one reaction mechanism, the C(sp3)–H bond of allyl-substituted 3,4-dienoate is first activated while the C(sp)–H bond of alkyne is first activated in the other reaction mechanism. It is found that the activation of C(sp)–H bond of alkyne is superior to C(sp3)–H bond activation of allyl-substituted 3,4-dienoate. The calculations suggest that the reaction mainly proceeds via C(sp)–H bond activation, CO insertion, alkene insertion, second CO insertion, allene CC insertion and C(sp3)–H bond activation steps. The transition states of alkene insertion and CO insertion into Pd-C(sp3) are competitive as the rate-determining transition state with a free energy barrier of around 23 kcal/mol. Moreover, it is found that the CO molecule does not directly participates in the reaction but also acts as an ancillary ligand. In addition, the reaction mechanisms for formation of other side products have been calculated and compared.