A plausible mechanism for copper-catalyzed oxidative chlorophenol couplingreactions. Semi-empirical AM1 and ab initio 3-21G molecular orbital studies

Semi-empirical AM1 and ab initio molecular orbital calculations were perfor med to gain more insight into the mechanism of copper-catalyzed oxidative p henol coupling reactions. Partial charges were determined for chlorophenols , chlorophenolate anions, chlorophenoxy radicals and chlorophenoxonium cati ons tin both the singlet and triplet states) at the AM1 level. Calculations of these species indicate that the only aromatic carbon bearing a substant ial positive charge is the para carbon of the cation in the singlet state. The results support a mechanism for copper-catalyzed oxidative phenol coupl ing in which dinuclear phenolate-bridged copper(II) species act as intermed iates affording chlorophenoxonium cations after a double-bond one-electron transfer. (C) 1999 Elsevier Science Ltd. All rights reserved.