Synthesis and ESR studies of redox reactivity of bis (3,5-di-tert-butyl-1,2-benzoquinone-2-monooximato)Cu(II)

Complexing of 3,5-di-tert-butyl-1,2-benzoquinone-2-monooxime with Cu(II) in air and under N-2 gave Cu(qo)(2) and Cu(qo)(2). H2O (where go is 3,5-di-te rt-butyl-1,2-benzoquinone-2-monooximato-anion) complexes, respectively. The ESR spectroscopy showed that the reduction of these complexes with P(PhX)( 3) (X = H, m-Cl, m-CH3, p-Et2N-) and 1,4-bis(diphenyldiphosphino) butane (d ppb) proceeds via the radical formation (phenoxazine, amino phenoxy and nit rene type radical intermediates) and pathways of reduction depend on the st ructure of these complexes. The reaction of Cu(qo)(2) with dppb and P(PhX)3 phosphines gave essentially identical ESR spectra. At the same time, reduc tion of Cu(qo)(2). H2O with PPh3 result in entirely different unstable radi cal spectrum (g = 2.0046) which is further converted to another relatively stable Cu-containing radical signal (g = 2.0052). The unstable radical spec ies attributed to nitrene type radicals. The initial complexes and all radi cal products were characterized by their ESR and optical spectra. (C) 2000 Elsevier Science B.V. All rights reserved.