Synthesis, characterization and reactivity of a series of dinuclear copper complexes bearing the ligand bis[3-(2-hydroxybenzylideneamino)phenyl] sulfone and derivatives

The ligands bis[3-(X-2-hydroxybenzylideneamino)phenyl] sulfones (X = none: BHBAPS, X = 3-tert-butyl: BH(t-Bu)BAPS and X = 3,5-dichloro: BHCl(2)BAPS) were prepared. These, together with Cu(OAc)(2) were used in the syntheses of the dinuclear copper complexes Cu-2(BBAPS)(mu -OMe)(2) (1), Cu-2[B(t-Bu)BAPS] (mu -OH)(2) (2), and Cu-2[BCl(2)BAPS] (mu -OMe)(2) (3). Complex 1 was crystallographically characterized. The structures of 2 and 3 are similar to 1 by comparison of IR, UV-Vis, FAB-MS and elemental analyses results. Complexes 1-3 (1 mol%) were used in the oxidation of 2,4- and 2,6-di-t-butylphenol (dtbp) at -50 degreesC with H2O2. The results show that (1) the coupling products are preferred when CH2Cl2 is used; and (2) the quinone yield increases when THF is utilized. In CH2Cl2 with 2,4-dtbp, the yield of the coupling product based on the complex amount, is in the order 2, 1, and 3 with yields of 6300, 4700 and 200%, respectively, Low temperature UV-Vis results of the reaction of 1 with H2O2 showed the growth of peaks at 390 and 580 nm indicative of a mu-eta (2):eta (2)-peroxo or mu-eta (1):eta (1)-hydroperoxo intermediate. At -50 degreesC, this spectrum does not change. But when warmed to 0 degreesC, a spectrum similar to the original spectrum was obtained. This probably indicates hydrogen radical abstractions of the peroxo intermediate from solvents, and if excess H2O2 is present, the peroxo intermediate may again be formed. This reusability of the complex explains the high yield using 1 and 2. (C) 2001 Elsevier Science B.V. All rights reserved.