Synthesis and characterisation of platinum(II) complexes of 1-methyl-2- { (arylazo)imidazoles} and their dioxolene derivatives

368-3731-Methyl-2-(arylazo)imidazoles, p-R-C6H4-N=N-C3H2 N2 -1-CH3, (RaaiMe (1); R = H(a), Me(b), Cl (c) have been treated with K2PtCl4 to synthesise brown-red Pt(RaaiMe)Cl2 (2) complexes. Addition of dioxolene in the presence of Et3N to CHCl3 - MeOH solution of Pt(RaaiMe)Cl2 yield green coloured mixed complexes of the composition [Pt(RaaiMe)(O,O)] (O,O = catecholate (cat) (3); 4-tert-butylcatecholate (tbcat), (4); 3,5-di-tert-butylcatecholate (dtbcat), (5); tetracholorocatecholate (tecat), (6) ). The complexes have been characterised by elemental analyses, IR, UV-Vis-NIR and 1H NMR spectral data. The solution electronic spectra exhibit ligand-to- ligand charge transfer (LLCT) transition at red to NIR region; the position and symmetry of the band depend on the substituent type on the dioxolene and arylazoimidazole frames. This is qualitatively assigned as HOMO(dioxolene)→ LUMO(RaaiMe). Cyclic voltammogram shows consecutive oxidation of catechols to semiquinone and semiquinone to quinone and azo reductions. The difference in first oxidation and reduction potential is linearly related with LLCT transition energy. The comparison of the physical properties of present series of complexes with palladium(II )-analogues show the involvement of Pt(II )-dπ orbitals to stabilise the complexes