Iridium mediated phenolic O-H activation and cyclometalation of 2-(naphthyl-1′-azo)-4-methylphenol — Formation of organoiridium complexes

Abstract

Reaction of 2-(naphthyl-1′-azo)-4-methylphenol with [Ir(PPh3)3Cl] in refluxing ethanol in the presence of a base (NEt3) affords an organoiridium complex of type [Ir(PPh3)2(L)(H)], where L represents the coordinated 2-(naphthyl-1′-azo)-4-methylphenolate ligand. A similar reaction carried out in toluene affords the [Ir(PPh3)2(L)(H)] complex along with a similar complex of type [Ir(PPh3)2(L)Cl]. Structures of both the [Ir(PPh3)2(L)(H)] and [Ir(PPh3)2(L)Cl] complexes have been determined by X-ray crystallography. In both the complexes, 2-(naphthyl-1′-azo)-4-methylphenol is coordinated to iridium, via C-H activation at the 2′ position of the naphthyl ring, as a dianionic tridentate C, N, O-donor and the two triphenylphosphines are trans. The organoiridium complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ir(PPh3)2(L)(H)] and [Ir(PPh3)2(L)Cl] complexes shows a reversible Ir(III)-Ir(IV) oxidation respectively at 0·55 and 0·73 V vs SCE. An irreversible oxidation of the coordinated 2-(naphthyl-1′-azo)-4-methylphenolate ligand is observed above 1·0 V vs SCE and an irreversible reduction of the same is observed near −1·0 V vs SCE.