H-bonding and steric effects on the properties of phenolate and phenoxyl radical complexes of Cu(II).

Herein, the N-R substituted N,O-phenol-pyrazole redox-active pro-ligands, (R)LH (R = Me, Pr) are reported together with their corresponding bis-Cu(R)L(2) complexes (2 and 3, respectively). The latter are reversibly oxidised to the corresponding stable Cu(II)-phenoxyl radical complexes 2(+) and 3(+). The properties of the tetrahedrally distorted complexes 2 and 3 (and those of 2(+) and 3(+)) are being compared to those of the square-planar H-bonded complex 1 (bis-Cu(H)L(2)) and those of 1(+). These studies have permitted H-bonding and steric effects on the redox, spectroscopic and chemical properties of Cu(II)-phenolate and Cu(II)-phenoxyl radical species to be established.