Issue 8, 2012

Recent advances on the chemistry of transition metal complexes of 2-(arylazo)pyridines and its arylamino derivatives

Abstract

Recent advancement on the redox properties of a selection of transition metal complexes of the azoaromatic ligands: bidentate L1 [2-(arylazo)pyridine] and tridentate HL2 [2-(aminoarylphenylazo)pyridine] are described and compared. Due to the presence of a low lying azo-centered π*-orbital, these azoaromatic ligands may exist in multiple valent states. The coordination chemistry of the L1 ligands was thoroughly studied during the 1980s. These complexes undergo facile reduction in solution at low accessible potentials. One electron reduced azo-complexes, though known for a long time to occur in solution, have only recently been isolated in a crystalline state. New synthetic protocols for the synthesis of metal-bound azo-radical complexes have been developed. Low-valent metal complexes such as metal carbonyls have been found to be excellent starting materials for this purpose. In a few selected cases, syntheses of these complexes were also achieved from very high valent metal oxides using triphenylphosphine as both a reducing and oxo-abstracting agent. Issues related to the ambiguities of the electronic structures in the azo-metal complexes have been discussed considering bond parameters, redox and spectral properties. Unusual redox events such as RIET (Redox-Induced Electron Transfer) phenomena in a few systems have been elaborated and compared with the known example. Novel examples of N[double bond, length as m-dash]N bond cleavage reactions via four-electron reduction and subsequent C–N bond formation in metal-bound coordinated ligands have been noted.

Graphical abstract: Recent advances on the chemistry of transition metal complexes of 2-(arylazo)pyridines and its arylamino derivatives

Article information

Article type
Perspective
Submitted
26 May 2011
Accepted
23 Nov 2011
First published
05 Jan 2012

Dalton Trans., 2012,41, 2213-2226

Recent advances on the chemistry of transition metal complexes of 2-(arylazo)pyridines and its arylamino derivatives

S. Samanta, P. Ghosh and S. Goswami, Dalton Trans., 2012, 41, 2213 DOI: 10.1039/C2DT10986G

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