Sandmeyer reactions. Part 1. A comparative study of the transfer of halide and water ligands from complexes of CuII to aryl radicals

Abstract

Rate constants have been estimated for the transfer to aryl radicals of Cl ligands from CuCl⁺ and CuCl₂ relative to that for the transfer of water ligands from Cu²⁺: k^OH:k₁^Cl:k₂^Cl= 1 : (59.3 ± 3.4): (205 ± 9) The rate data indicate that aryl radicals exhibit nucleophilic character during these ligand transfers and that, in the competition between chlorination and hydroxylation, the reactivity–selectivity principle is not obeyed. In competition between CuBr⁺ and CuCl⁺ in transferring halide ligands to 4-chlorophenyl radicals a value of k₁^Br/k₁^Cl= 2.3 is estimated; there is no selectivity between bromination and chlorination across a range of aryl radicals. The reactivities of the different copper complexes in ligand-transfer broadly parallel their reduction potentials. The nature of the transition state for ligand-transfer is discussed.