Chemically Induced Cyclometalation of 2-(Arylazo)phenols. Synthesis, Characterization, and Redox Properties of a Family of Organoosmium Complexes GuptaParna ButcherRay J. BhattacharyaSamaresh 2003 Reaction of 2-(arylazo)phenols (H<sub>2</sub>ap-R; R = OCH<sub>3</sub>, CH<sub>3</sub>, H, Cl, and NO<sub>2</sub>) with [Os(PPh<sub>3</sub>)<sub>2</sub>(CO)<sub>2</sub>(HCOO)<sub>2</sub>] affords a family of organometallic complexes of osmium(II) of type [Os(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-R)] where the 2-(arylazo)phenolate ligand is coordinated to the metal center as a tridentate C,N,O-donor. Structure of the [Os(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-H)] complex has been determined by X-ray crystallography. All the [Os(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-R)] complexes are diamagnetic and show characteristic <sup>1</sup>H NMR signals and intense MLCT transitions in the visible region. They also show emission in the visible region at ambient temperature. Cyclic voltammetry on the [Os(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-R)] complexes shows a reversible Os(II)−Os(III) oxidation within 0.39−0.73 V vs SCE, followed by a reversible Os(III)−Os(IV) oxidation within 1.06−1.61 V vs SCE. Coulometric oxidation of the [Os(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-R)] complexes generates the [Os<sup>III</sup>(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-R)]<sup>+</sup> complexes, which have been isolated as the hexafluorophosphate salts. The [Os<sup>III</sup>(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-R)]PF<sub>6</sub> complexes are one-electron paramagnetic and show axial ESR spectra. In solution they behave as 1:1 electrolytes and show intense LMCT transitions in the visible region. The [Os<sup>III</sup>(PPh<sub>3</sub>)<sub>2</sub>(CO)(ap-R)]PF<sub>6</sub> complexes have been observed to serve as mild one-electron oxidants in a nonaqueous medium.