Synthesis, spectral characterisation and electrochemical studies of dichloro-{1-benzyl-2-(arylazo)imidazole}platinum(II) complexes and their dioxolene derivatives

1-Benzyl-2-(arylazo)imidazoles, p-RC6H4N=NC3H2-N-2-1-CH2Ph [RaaiBz (2); R=H (a), Me(b), Cl(c)], react with K2PtCl4 in boiling MeCN-H2O (1:1 v/v) to giv e brownish-red Pt(RaaiBz)Cl-2 (3) complexes. Addition of dioxolene in the p resence of Et3N to a CHCl3-MeOH solution of Pt(RaaiBz)Cl-2 yields green mix ed complexes of composition [Pt(RaaiBz)(O,O)] [O,O = catecholate (cat) (4); 4-tert-butylcatecholate (tbcat), (5); 3,5-di-tert-butylcatecholate (dtbcat ), (6); tetracholorocatecholate (tccat), (7)] which were characterised by e lemental analyses, i.r., u.v.-vis.-near i.r. and H-1-n.m.r. spectral data. The solution electronic spectra exhibit ligand-to-ligand charge-transfer (l .l.c.t) transitions in the red to near i.r. region; the position and symmet ry of the band depend upon the substituent on the dioxolene and arylazoimid azole. This effect is qualitatively assigned as HOMO(dioxolene) --> LUMO(Ra aiBz). A cyclic voltammogram of the dioxolene complex reveals two consecuti ve oxidative couples corresponding to catechols to semiquinones and semiqui none to quinone, respectively and the reductive couples represent azo reduc tions.