Cyclic voltammetric and e.s.r. studies of a tetraaza 14-membered macrocyclic copper(II) complex derived from 3-salicylideneacetylacetone ando-phenylenediamine: stabilization and activation of unusual oxidation states

Summary A 14-membered macrocyclic Schiff base derived from 3-salicylideneacetylacetone ando-phenylenediamine acts as a tetradentate and strongly conjugated ligand to form a cationic solid complex with CuCl₂. U.v.-vis. and e.s.r. spectral data reveal a strong ligand to metal -interaction in the square planar complex. C.v. data reveal that the title ligand is able to stabilize the copper(III) oxidation state more effectively than comparable saturated or partially unsaturated macrocyclic ligands and confers a weaker tendency for reduction of copper(II) to copper(I) and copper(0). While the inclusion of a PPh₃ ligand suppresses the Cu⁰ Cu^I Cu^II oxidation, imidazole and pyridine strongly enhance the Cu^II Cu^III oxidation of the complex.