Osmium and cobalt complexes incorporating facially coordinated N,N,O donor azo-imine ligands: Redox and catalytic properties

Reactions of 1-{[2-(arylazo)phenyl]iminomethyl}-2-phenol, HL [where H represents the dissociable phenolic protons of ligands and aryl groups of HL are C6H5 (HL1), p-CH3C 6H5 (HL2), p-ClC6H5 (HL3)] with Os(H)(CO)(Br)(PPh3)3 in toluene and with Co(ClO4)3.6H2O in methanol afforded new facially coordinated complexes of composition [(L)Os(CO)(Br)(PPh3)] and [(L)2Co]ClO4. The anionic ligand (L) -, binds the metal in tridentate (N, N, O) manner in [(L)Os(CO)(Br)(PPh 3)] and [(L)2Co]ClO4 complexes. All the Os(II) and Co(III) complexes are diamagnetic and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. The cyclic voltammograms exhibited one quasi reversible oxidative response near 0.10 V vs SCE for [(L)Os(CO)(Br)(PPh3)] and [(L)2Co]ClO4 complexes displayed serial reductive responses within - 0.06 to - 1.61 V vs SCE. Single point DFT calculation was carried out to examine the nature of redox orbitals. Conversion of ketones to corresponding alcohols has been studied using [(L)Os(CO)(Br)(PPh3)] as catalyst.