Catalytic oxidative reactions of organic compounds by nitrogen-containing copper complexes

The dimeric copper(II) complex di-mu-chloro-bis[chloro(di-3,5-dimethylpyrazole)copper(II)] (A) in the presence of co-oxidant hydrogen peroxide acts as a catalyst for the oxidation of benzylic alcohols to give the corresponding aldehydes. In the presence of hydrogen peroxide it also catalyses the oxidation reaction of 2,6-dimethylphenol to 4,4-dihydroxy-3,5,3',5'-tetramethylbiphenyl. The oxidative reactions by bis-pyridinium tetrachlorocopper(II) (B) in the presence of hydrogen peroxide were compared for similar catalytic reactions of A, and it is observed that B can catalyse the oxidation of aromatic diols, 2,6-dimethylphenol and thiophenol, but is not suitable for oxidation of benzylic alcohols. Bis-(N-phenyl-3,5-dimethylpyrazole)copper(II) nitrate monohydrate (C) has a suitable redox potential for one-electron oxidation. It can oxidize ferrocene to the ferricinium. cation, and it can liberate bromine from tetra-alkylammonium bromides. The complex is catalytically effective for the oxidation of different aromatic and aliphatic aldehydes to the corresponding carboxylic acids. The compound is also effective in transforming benzylic amine to benzylalcohol and benzaldehyde. It can also oxidize diphenylmethane to give benzophenone and diphenylmethanol. It is observed that in each of these complexes a quasi-reversible Cu(I)-Cu(II) species is present and facilitates the single-electron oxidation process. Copyright (C) 2004 John Wiley Sons, Ltd.