New copper(II) species from the copper/2,2′-bypyridine and copper/4-dimethylaminopyridine catalyzed aerobic alcohol oxidations

It is known that both Cu/BPY/TEMPO and Cu/DMAP/TEMPO are efficient catalyst systems for the aerobic oxidations of alcohols (BPY: 2,2'-bipyridine; DMAP: 4-dimethylaminopyridine; TEMPO: 2,2,6,6-tetramethylpiperidinyl-1-oxyl), the reactivity difference between the two systems and relevant copper species involved in the catalysis are, however, scarcely investigated. In this work, we attempted to isolate and characterize new possible Cull species participating in the catalytic reactions, and compared the catalytic aerobic oxidation of benzylic alcohol in the presence of both catalyst systems under similar conditions. In addition to the isolation of a new ionic complex from the Cu/DMAP/TEMPO reaction system in CH2Cl2-MeOH, a dinuclear Cu-II complex different from all previously reported species is observed from a separate experiment while performed in CH3CN. Another structurally related dinuclear Cu-II complex of BPY is also isolated from the Cu/BPY/TEMPO mediated reaction. The catalytic reactivity of both in-situ formed catalysts and isolated Cu-II complexes is tested towards the aerobic oxidation of benzylic alcohol. (C) 2015 Elsevier Ltd. All rights reserved.