Studies on aerobic reactions of ammonia/3,5-di-tert-butylcatechol Schiff-base condensation products with copper, copper(I), and copper(II). Strong copper(II)-radical ferromagnetic exchange and observations on a unique N-N coupling reaction

Stoichiometric quantities of 3,5-di-tert-butylcatechol and aqueous ammonia react in pyridine solution to form 2-amino-4,6-di-tert-butylphenol. Under an atmosphere of dioxygen the aminophenol is oxidized to either the corresponding iminosemiquinone or iminobenzoquinone. In the presence of Cu(II) iminosemiquinone condensation with the aminophenol gives the Cat-N-SQ radical ligand obtained as the Cu(py)(2)(Cat-N-SQ) complex. Metal and ligand magnetic orbitals are orthogonal and couple ferromagnetically to give a S = 1 molecular spin state at temperatures up to 300 K. In nonpolar solvents the complex undergoes ligand oxidation and disproportionation to give Cu(Cat-N-BQ)(2). Crystallographic characterization on crystals obtained as the i-propanol solvate [orthorhombic, C222(1), a = 19.548(3) Angstrom, b = 24.536(5) Angstrom, c = 23.655(5) Angstrom, V = 11346(4) Angstrom(3), Z = 8, R = 0.068] show that the expected Jahn-Teller distortion appears in the trans Cu-O lengths of the equatorial plane rather than for the axial Cu-N lengths. Reactions carried out with both Cu(I) and Cu metal require metal oxidation to give the Cu(II) products obtained. With metallic Cu this occurs by a reaction with iminoquinone to give bis(iminosemiquinone)copper(II). Further reaction of this product with aminophenol gives Cu(py)(2)(Cat-N-SQ) by condensation, and, with O-2, oxidation gives a coordinated azophenolate ligand in Cu(py)(azophenolate) by a unique N-N bond-forming reaction. Cu(py)(azophenolate) has been characterized crystallographically [monoclinic, P2(1)/n, a 10.990(2) Angstrom, b = 10.736(3) Angstrom, c = 26.848(4) Angstrom, beta = 98.09(1)degrees, V = 3136(1) Angstrom(3), Z = 4, R = 0.048].