Aerobic alcohol oxidation with cationic palladium complexes: insights into catalyst design and decomposition

Aerobic alcohol oxidation catalyzed by the newly synthesized dimeric [(neocuproine)Pd(mu-OAc)](2)(OT)(2) (I; neocuproine = 2,9-dimethyl- 1, 1 0-phenanthroline) proceeds under exceptionally mild conditions (room temperature, ambient air) compared to those required for the previously reported monomeric diacetate analogue (neocuproine)Pd(OAc)(2) (2) and the monomeric ditriflate analogue (neocuproine)Pd(MeCN)(2)(OTf)(2) (3). An unprecedented initial turnover frequency (TOFi) for such mild conditions (78 (Pd atom)(-1) h(-1)) is observed with catalyst 1; however, competitive oxidation of a methyl group on the ligand to a carboxylate group results in catalyst inactivation. During the study of 1, we isolated for the first time [(neocuproine)Pd(mu-OH)](2)(OTf)(2) (4), a possible intermediate in the catalytic cycle, and we report its crystal structure and catalytic activity herein.