Osmium-Promoted Oxidative Dimerization of Aminoarenes toN-Aryl-o-arenoquinone Diimines (L). Synthesis, Structure, Electrochemistry, and Reactivity of OsBr₂L₂

Abstract

A family of o-arenoquinone diimine chelates, OsBr(2)L(2) (1, L = N-aryl-o-arenoquinone diimine), were isolated from the reaction of (NH(4))(2)OsBr(6) and primary aromatic amines, Ar-NH(2). These complexes constitute the first examples of osmium compounds of the o-benzoquinone diimine family. The above oxidative dimerization reaction of Ar-NH(2) was authenticated by the X-ray structure determination of a representative example. The X-ray structure of OsBr(2)L(2) (R = H) revealed a cis geometry with respect to two coordinated bromides. The bond length trends within the chelate as well as the aromatic rings are consistent with a diimine character of the ligand bound to osmium in its bivalent oxidation state. The complexes showed multiple transitions in near-IR and visible regions. These are electroactive and undergo multiple electron transfer. Three successive voltammetric responses, two oxidative and one reductive, were observed. The potential range was +1.7 to -0.8 V vs SCE in CH(3)CN solution (Pt electrode). The potentials of the above responses for differently substituted compounds depend on the Hammett summation operatorsigma(p) parameters of the substitution on L. The EPR spectrum of the electrogenerated 1-electron-oxidized complex 1a(+) is described. The electrode potentials of 1 are compared with those of related systems. A qualitative correlation between Os-N bond distances and Os(III)/Os(II) formal potentials for the Os(II) compounds of three different N,N donors is noted. The synthesis of a mixed-ligand tris chelate, [Os(bpy)L(2)](ClO(4))(2).H(2)O, is described, involving the reaction of 1 equiv of 1 with 2 equiv of Ag(bpy)(2)(+). The redox properties of the tris complex are reported. Crystal data for OsBr(2)L(2) (R = H) are as follows: empirical formula C(24)H(20)Br(2)N(4)Os; crystal system triclinic, space group P&onemacr;; a = 10.464(6) Å, b = 11.778(6) Å, c = 12.595(10) Å; alpha = 103.86(5) degrees, beta = 112.72(6) degrees, gamma = 107.79(4) degrees; V = 1245.3(10) Å(3); Z = 2; R = 4.46%; R(w) = 5.21%.

A Novel Dinuclear Ruthenium Complex Bridged through a Substituted Phenazine Ligand Formed by Ruthenium-Promoted Oxidative Assembly of 1,3-Diaminobenzene

“…It was possible to propose both the composition and structure of the intermediate 2 , from the identity of 3 , and from the comparison of physicochemical data of 2 and 3 . From the foregoing discussion it should be clear that while complex 1 is a congener of the reported diimine complexes [Ru(acac) 2 (diim)] (diim= N ‐phenyl‐(1,2‐benzoquinone)diimine),3a obtained from the reaction of [Ru(acac) 3 ] and ArNH 2 , the dimetallic complexes obtained here are formed by previously unknown organic transformations.…”

“…Solvents and chemicals used for syntheses were of analytical grade. The supporting electrolyte (tetraethylammonium perchlorate) and solvents for electrochemical work were obtained as before 3a…”

“…A Perkin–Elmer 240C elemental analyzer was used to record microanalytical data. Electrochemical measurements were done under a dry nitrogen atmosphere on a PAR 370‐4 electrochemistry system as described earlier 3a. All potentials in this work are referenced to the saturated calomel electrode (SCE) and are uncorrected for junction contribution.…”

Design and synthesis of multidentate ligands via metal promoted C-N bond formation processes and their coordination chemistry

“…In these reactions, the metal ion acts as mediator, which in fact forms the basis of homogeneous catalysis. We have been interested [6][7][8][9][10][11] in transition metal promoted transformations in the context of design and synthesis of new organic ligands and to study their coordination chemistry. In this presentation we wish to discuss some of our recent results [12][13][14][15][16] on aromatic ring amination reaction of coordinated 2-(phenylazo)pyridine (pap).…”

Ferric-Chloride-Promoted Oxidation ofp-Anisidine to anN-Substituted Phenazine Derivative − Structural Elucidation, Protic Equilibria and Coordination Chemistry of the Phenazine

“…In this respect, we have recently reported [1Ϫ3] the ruthenium(III)-and osmium(IV)-mediated ortho dimerisation of primary aromatic amines, ArNH 2 , leading to N-aryl-1,2-diimino arenes [Equation (1)]. It may be relevant to add here that complexes of quinone-related 1,2-diimine ligands are of interest [4,5] in contemporary research and that N-substituted 1,2-diimino complexes of the above type were not possible to synthesise by conventional synthetic routes.…”