Interaction of 2-(arylazo)phenols with rhodium. Usual coordination vs. C-H and C-C activation

Baksi, S., Acharyya, R., Dutta, S., Blake, A.J., Drew, M.G.B. and Bhattacharya, S. (2007) Interaction of 2-(arylazo)phenols with rhodium. Usual coordination vs. C-H and C-C activation. Journal of Organometallic Chemistry, 692 (5). pp. 1025-1032. ISSN 0022-328X doi: 10.1016/j.jorganchem.2006.10.063

Abstract/Summary

Reaction of 2-(2'-hydroxyphenylazo)phenol with [Rh(PPh3)(3)Cl] in refluxing benzene in presence of triethylamine afforded a red complex in which the ligand is coordinated to rhodium as a tridentate O,N,O-donor. However, similar reaction of [Rh(PPh3)(3)Cl] with 2-(2'carboxyphenylazo)-4-methylphenol yielded two complexes, viz. a blue one and a green one. In both the complexes the ligand is coordinated as C,N,O-donor. However, in the blue complex orthometallation takes place from the ortho-carbon atom, which bears -COOH group via decarboxylation and in green one orthometallation occurs from the other ortho-carbon. Structures of all the three complexes were determined by X-ray crystallography. In all the three complexes rhodium is sharing the equatorial plane with the tridentate ligand and a chloride, and the two triphenylphosphines are axially disposed. All of the complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE and a reduction of the coordinated azophenolate ligand on the negative side. (c) 2006 Elsevier B.V. All rights reserved.