Azo Appended Modified Lawsone Derived Ru‐Systems with Multi‐Redox Entities. Competitive Electronic Form and the Question of Azo Reduction

Abstract

The article dealt with the ruthenium complexes of redox active azo appended modified lawsone L 1 À (HL 1 : (E)-2hydroxy-3-(p-tolyldiazenyl)naphthalene-1,4-dione))/L 2 À (HL 2 :5-À and L 2 À differed with respect to the para-quinone versus phenazine moieties linked to the azo function. Structural analysis of the complexes established unreduced state of the azo (N=N) group of coordinated L 1 À /L 2 À or pap as well as unprecedented para-quinone form of L 1 À . The involvement of selective redox center(s) towards the accessible redox steps of the complexes encompassing multiple redox active entities i. e. Ru, phenolate (L 1 À /L 2 À ), para-quinone (L 1 À ), phenazine (L 2 À ), azo (L 1 À /L 2 À , pap), diimine (bpy) was analyzed by combined experimental and DFT calculations. It revealed that under the prevailing competitive scenario oxidation was mostly dominated by the phenolate group of L 1 À /L 2 À (phenolate!phenoxide), while successive reductions were taken place either at the para-quinone/phenazine units of L 1 À /L 2 À or azo/diimine functions of pap/bpy. Though the azo function of pap in 3 + /7 + underwent facile reduction, the same azo function associated with L 1 À /L 2 À conspicuously remained unreduced in all occasions. The frontier molecular orbital analysis revealed that the propensity of pap for the azo reduction with special reference to that in L 1 À /L 2 À could be correlated with its relatively lower energy π* orbital (LUMO). Complexes displayed intense LMCT (1/5) and bpy (2 + /6 + ), pap (3 + /7 + ), L (4/8) targeted MLCT transitions in the visible region.

Tetracoordinated 15-Electron Ruthenium(I) in a Discrete Triruthenium Framework

“…(i) Ligand (L)-based oxidation (O1) 6b and Ru III -based reduction (R1) of 1 + /4 + (S = 1 / 2 ) led to the electronic forms of [A 2 Ru III L •+ ] 2+ and [A 2 Ru II (L)] for 1 2+ /4 2+ and 1/4 (S = 0), respectively, revealing redox noninnocence of L with special reference to its oxidation event. 13 Interestingly, oxidized 1 2+ (S = 1) and 4 2+ (S = 0) differed with respect to their spin configurations. The unstable feature of 1 2+ (S = 1) on CV or the electrolysis time scale precluded to check its EPR signature.…”