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, ^RLH (R = Me, Pr) are reported together with their corresponding bis-Cu^RL₂ 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 ^HL₂) 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.