Isomeric mixed dioxolene 2-(arylazo)pyridine complexes of osmium(II): Synthesis, spectra and electrochemistry

Abstract

The complexes blue-violet (<b>3</b>) and red-violet (<b>4</b>) isomers of [OsX₂L₂] [X = Cl or Br; L (<b>2</b>) = 2-(phenylazo)pyridine (L¹ and 2-(<i>m</i> -tolylazo)pyridine (L²)] react smoothly with catechol and its substituted derivative [H₂Q; (<b>1</b>)] in boiling aqueous ethanol affording mixed tris complexes of the type [OsQL₂] [(<b>5</b>) and (<b>6</b>), respectively]. The new complexes have been characterized by physicochemical, spectroscopic and magnetic methods. From ¹H NMR spectra (taking δ_Me of L² as diagnostic probe), the stereoretentivity of the reactions is proposed. The diamagnetic complexes display a number of spinal lowed and spin-forbidden charge-transfer transitions in the 1200-200 nm range. Both (<b>5</b>) and (<b>6</b>) are electroactive and display six voltammetric responses - two oxidati ons and four reductions. EPR study of the coulometrically generated one electron oxidation product suggests the involvement of semiquinone radical formation.