CATALYTIC ACTIVITY OF HYDROXO-BRIDGED CU(II) COMPLEXES WITH NITROGEN CHELATING LIGANDS IN THE HOMOGENEOUS AUTOXIDATION OF 2,6-DI-T-BUTYLPHENOL

Complexes of the type [Cu2(mu-OH)2(L-L)2]X2.nH2O [L-L = bipy or substituted bipy; phen or substituted phen; dipyam (2,2'-dipyridylamine); X = Cl-, Br-, I-, N02-, NO3-, ClO4-, SO42-; n = 0-->5] have been studied as catalysts for the autoxidation of di-tert-butylphenol to the corresponding diphenoquinone. The activity depends strongly both on the L-L ligand and the counter-ion. The addition of Cl- in a 1:1 molar ratio to copper largely improves the diphenoquinone yields. Small amounts of water slightly favour the diphenoquinone formation; by contrast, an excess of ligand inhibits the reaction and can also suppress it. The best catalysts have been found to be the dipyam halide derivatives. Experimental conditions are mild: good catalytic activity was observed even at 20-degrees-C under atmospheric pressure of oxygen.