Polymer-supported cobalt(II) tetraaza macrocyclic complexes and their reaction with dioxygen

Abstract

Four cobalt(II) tetraaza macrocyclic complexes of the ‘lacunar cyclidene’ type have been prepared, including two new, unbridged, examples. The reactions of these complexes with oxygen have been investigated, either in solution, in a mixture of acetonitrile–pyridine (4 : 1 v/v), or when dispersed in the matrix of a copolymer containing 4-vinylpyridine (vpy), dissolved in dichloromethane. Three different copolymers have been used as supporting matrices (vpy content in parentheses); vpy–styrene (6.2), –methyl methacrylate (5.2) and –butyl methacrylate (15.2%). The oxygenation reactions have been studied both by ESR spectroscopy of frozen solutions and by electronic spectroscopy at or near room temperature. The presence of the polymeric supports has a marked influence on both the formation of Co–O₂ adducts and their stability with respect to autoxidation. The polymer-supported ‘copoly complex’ oxygen adducts have much greater lifetimes than those of the O₂ dioxygen adducts of the same complexes ‘free’ in solution. The results are discussed in terms of the complex structure, polymer type and the temperature of the reaction.