Mechanistic Insight on the Aerobic Oxidation of Alcohols by Trivalent Copper from DFT Calculations

Density functional theory (DFT) calculations were carried out to elucidate the mechanism of alcohol oxidation by a Cu(III) anilidosalen complex. The study considered singlet, broken‐symmetry singlet, and triplet states. During the first step the alcoholate binds to the copper, inducing valence tautomerism, transforming the Cu(III) complex into a Cu(II)‐alkoxyradical adduct. Subsequently, an “aniline” ring s a hydrogen from the substrate with a low barrier, yielding a Cu(I) aniline complex and the aldehyde, akin to galactose oxidase. Catalyst re‐oxidation is coupled to dioxygen reduction. Initially, dioxygen is reduced by Cu(I) into superoxide, which binds to the metal. Protonation then yields either a Cu(II)‐hydrosuperoxo or a Cu(III)‐hydroperoxo adduct. Further protonation closes the catalytic cycle by releasing hydrogen peroxide. The alcoholate binds to the copper, transforming the Cu(III) complex into a broken symmetry Cu(II)‐alkoxyradical adduct. Next, H‐atom ion by the anilido moiety directly yields the reduced catalyst and the aldehyde.