Formation of a Cu(II)-phenoxyl radical complex from a Cu(II)-phenolate complex: A new model for galactose oxidase

A new N3O type tetradentate ligand (HL) [2,4-di-tert-butyl-6-((4-(2-(6,8-di-tert-butyl-2H-benzo[e] [1,3]oxazin-3(4H)-yl)ethyl)piperazin-1-yl)methyl)phenol] and its complex [CuL(CH3OH)]ClO4 (CH3OH) have been synthesised. The complex has been crystallographically and spectroscopically characterised. It has been noticed that in the presence of acetonitrile the Cu(II) centers in the complex undergo reduction with a concomitant oxidation of the ligand. EPR and UV-Vis spectroscopic studies of the complex in acetonitrile indicate that this disproportionation proceeds via the formation of a Cu(II)-phenoxyl intermediate. The Cu(II)-phenoxyl complex is found to be stable in methanol in the presence of base. The oxidised products of the ligand are isolated and characterized. The paramagnetic centers in the Cu(II)-phenoxyl complexes were found to be weakly ferromagnetically coupled. (C) 2013 Elsevier Ltd. All rights reserved.