Isolation and characterization of iridium(iii) and iridium(v) complexes of 2-(arylazo)pyridine and studies of amine fusion reactions at the coordinated diazo-ligand

Abstract

The reaction of IrCl₃·3H₂O with 2-(arylazo)pyridine (HL¹) in boiling methanol has afforded [Ir^IIICl₂(L¹)(HL¹)] (1) and [Ir^VCl₄(HL¹)]Cl (2). In complex 1, one of the two ligands [L¹]⁻ is orthometallated via coordination of an ortho-carbon of the aryl ring of [L¹]⁻ and one of the two azo nitrogens to form a five-membered chelate. X-Ray crystal structures of the two representative complexes, viz.1a and 2a, have been solved. Notably, the Ir–N length (2.140(3) Å) trans to the Ir–C bond in 1a is appreciably longer than the other three Ir–N lengths present in the same molecule. The N–N lengths in these two compounds lie close to that observed in the uncoordinated ligand. Thorough NMR studies were made to authenticate the carbon-bonded structure of compound 1a. In its ¹³C NMR spectrum, the resonance near δ 148 is assigned to the carbon bonded to the iridium metal center. UV-visible spectra along with the redox properties of these complexes are reported. The iridium(V) complex, 2 showed a reversible response near 1.40 V, presumably due to the iridium(V)–iridium(VI) couple. Several reductive responses at cathodic potentials, due to ligand reductions, were also observed. Metal promoted aromatic ring amination reactions at the coordinated HL¹ ligand in complexes 1 and 2 were investigated. The products were characterized using X-ray diffraction.