Chemically induced cyclometalation of 2-(arylazo)phenols. Synthesis,characterization, and redox properties of a family of organoosmium complexes

Reaction of 2-(arylazo)phenols (H(2)ap-R; R = OCH(3), CH(3), H, Cl, and NO(2)) with Os(PPh(3))(2)(CO)(2)(HCOO)(2)] affords a family of organometallic complexes of osmium(II) of type Os(PPh(3))(2)(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(3))(2)(CO)(ap-H)] complex has been determined by X-ray crystallography. All the Os(PPh(3))(2)(CO)(ap-R)] complexes are diamagnetic and show characteristic (1)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(3))(2)(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(3))(2)(CO)(ap-R)] complexes generates the Os(III)(PPh(3))(2)(CO)(ap-R)](+) complexes, which have been isolated as the hexafluorophosphate salts. The Os(III)(PPh(3))(2)(CO)(ap-R)]PF(6) 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(III)(PPh(3))(2)(CO)(ap-R)]PF(6) complexes have been observed to serve as mild one-electron oxidants in a nonaqueous medium.