Insight into copper oxidation catalysts: Kinetics, catalytic active species and their deactivation

The catalytic properties of in situ formed copper(II) complexes of N,N,N′,N′-tetramethylethylenediamine (TMEDA), rac-1,2-diaminocyclohexane (DACH) and 9,10-diaminophenantrene (DAPHEN) were investigated under optimized reaction conditions in the oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) with molecular oxygen in alkaline aqueous solutions. The kinetics of the reaction, catalytic species and their deactivation were studied, in order to clarify the reasons for low conversions in Cu(TMEDA) and Cu(DACH) catalyzed reactions. The most active catalyst was the scarcely soluble Cu(DAPHEN) with turn over number 5700 in the oxidation of veratryl alcohol. The catalytic precursors in Cu(TMEDA) catalyzed reactions is binuclear hydroxyl bridged complex (LCu-μ-(OH)2-CuL)2+. The main reason for the deactivation of these catalysts according to our results is the reactivity of the ligands under reaction conditions.