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

Abstract

1-Methyl-2-(arylazo)imidazoles, <i>p</i>-R-C₆H₄-N=N-C₃H₂ N₂<i> -</i>1-CH₃, (RaaiMe (<b>1</b>); R = H(<b>a</b>), Me(<b>b</b>), Cl (<b>c</b>) have been treated with K₂PtCl₄ to synthesise brown-red Pt(RaaiMe)Cl₂ (<b>2</b>) 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) (<b>3</b>); 4-<i>tert-</i>butylcatecholate (tbcat), (<b>4</b>); 3,5-di-<i>tert</i>-butylcatecholate (dtbcat), (<b>5</b>); tetracholorocatecholate (tecat), (<b>6</b>) ). 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.