Copper-catalyzed direct hydroxylation of arenes to phenols with hydrogen peroxide.

• Direct hydroxylation of arenes to phenols was reported. • A copper(II) complex of an N4 aminobenzimidazole was used as an efficient catalyst. • Hydrogen peroxide was used as a green oxidant. Direct hydroxylation of arenes to phenols with hydrogen peroxide as a green oxidant is an attractive approach. In the present study, we prepared several copper (II) complexes bearing tetra- (N4), tri- (N3) and pentadentate (N5) ligands, and the copperII-N4 complex could act as an efficient catalyst for hydroxylation of benzenes with H 2 O 2 (up to 22.4% yield of phenols with 10.0 equiv. H 2 O 2 , and 38.0% yield of phenol with limited amount of H 2 O 2) at room temperature. X-ray crystallographic analysis indicates that the CuII-N4 complex exhibits a square-pyramidal geometry and that two methyl groups connecting to the diamine are cis to each other. In comparison, copper(II) complexes supported by tri- (N3) and pentadentate (N5) ligands were also evaluated in the hydroxylation of benzene, demonstrating inferior performance. [Display omitted]. [ABSTRACT FROM AUTHOR]