Pd-mediated Activation of Molecular Oxygen

Heterogeneous catalytic systems involving palladium(II) diamine complexes have been used to successfully oxidize alcohols in the absence of copper co-catalyst with the use of molecular oxygen as a terminal oxidant. Recent attempts to determine the mechanism involved in these processes have varied. Our previous work has explained several aspects of the reaction mechanism including deprotonation of the alcohol, and the subsequent beta-hydride elimination step resulting in the formation of a palladium(II)hydride (L2PdH(X): X=OAc, Cl), but has heretofore ignored the role of O2.
The current mechanisms believed to be active in this process can easily be divided into two classes, those which employ palladium(0) and those which do not. One class of mechanisms requires the direct insertion of O2 in a palladium-hydride bond avoiding palladium zero altogether while the remaining proposals require the formation of palladium(0). Herein we investigate the interaction of O2 with palladium(II)hydride focusing on pathways which avoid and include palladium(0), and introduce some new aspects of the triplet-singlet crossover involved in this process.

Personnel: Robert (Smith) Nielsen and Jason Keith