Oxidative demethylation in monooxygenase model systems. Competing pathways for binuclear and helical multinuclear copper(I) complexes

The ligand 2,6-bis[N-(2-pyridylethyl)formimidoyl]-1-methoxybenzene (2,6-BPB-1-OCH3) (4) reacts with Cu(CH3CN)4BF4 to form novel binuclear copper(I) complexes [Cu2(2,6-BPB-1-OCH3)(BF4)2(CH3CN)4] (11) and [Cu2(2,6-BPB-1-OCH3)(BF4)2(CH2Cl2)0.5] (14), or the helical polynuclear copper(1) complex [Cu(2,6-BPB-1-OCH3)(BF4)]n (16). The complexes mimic certain monooxygenases as they rapidly take up O2 followed by demethylation of the anisole moiety (up to 95% yield). 18O experiments are provided that show competing aryl-oxygen (≥60%) and alkyl-oxygen (20%) bond cleavage pathways. Introduction of a p-methoxy substituent in the arene moiety of complex 11 decreases the oxygenation rate and led to an unprecedented O2 induced arene-OCH3-OCD3 exchange at 20 °C in CD3OD. A mechanistic rational is given.