Kedar Nath Mitra

A family of mixed ligand complexes of RuII-L [L = N-aryl-pyridine-2-aldimine], their reactions, isolation and characterization. X-ray crystal structure of [Ru(pic)(L1)2][ClO4]· CH2Cl2 [pic= 2-picolinate ion]

Abstract Synthesis of the tris-chelated complexes [Ru(L)n(L3)3−n]2+ (L= N-aryl-pyridine-2-aldimine, L3 = 2-(m-tolylazo)pyridine) based on silver(I) assisted trans-metallation is described. The complexes, [Ru(L)3]2+ and [Ru(L)(L3)2]2+ afford [Ru(pic)(L)2]+ and [Ru(pic)(L3)2]+ (pic= 2-picolinate ion) respectively, on hydrolysis and subsequent oxidation. When RuCl2(L)2 was reacted with two moles of [Ag(L3)2]+, a pink complex of composition [Ru(L)(L3)(L4)]+ [L4 = N-aryl-2-picolinamide] was isolated along with the expected brown complex, [Ru(L3)(L)2]2+. Initial oxidation of the metal ion favours L→L4 conversion. The complexes have been characterized using spectroscopy and X-ray crystallography. The X-ray structure of [Ru(pic) (L1)2]ClO4·CH2Cl2 is reported. The metal oxidation as well as ligand reductions for the complexes have been studied voltammetrically in acetonitrile using platinum as the working electrode. It has been observed that the oxidation of the transformed complexes, viz. [Ru(pic) (L)2]+, [Ru(pic)(L3)2]+ and [Ru(L)(L3)(L4)]+ occur at lower potentials as compared to their parent [Ru(L)n(L3)3−n]2+ complexes. All the complexes show metal-to-ligand charge transfer transitions in the visible range and absorption energies linearly correlate with the differences between the metal oxidation and the first ligand reduction potentials.

Two novel reactions of ruthenated aniline. Structure and bonding in bis-chelated ruthenium complexes of quinone related ligands

Two novel examples of oxidative ortho coupling of ruthenated aniline are described; the products are fully characterised by X-ray and other physicochemical data.

Synthesis, structure and redox properties of isomeric [RuCl2(L)2] (L=N-aryl-1,2-arylenediimine) complexes formed by the oxidative dimerization of coordinated aromatic amines

Abstract The di-arylamino complex [RuCl2(ArNH2)2L] (ArNH2=aromatic monoamine and L=N-aryl-1,2-diimino arene) reacts spontaneously with aqueous H2O2 to produce two isomers of [RuCl2(L)2] via oxidative dimerization of the two coordinated aromatic amines. The geometries of two isomers are cis with respect to two chlorides and are trans, cis(tc) and cis, cis(cc) in the following sequence: NH(imine), HN(imine) and ArN(imine), ArN(imine). Of the above two, the tc-[RuCl2(L)2] forms good X-ray quality crystals. The structure of a representative has been solved by X-ray diffraction. The geometry of the cc-[RuCl2(L)2] is, however, revealed by the spectral data. The tc-isomer possesses a C2-symmetry axis and the two-coordinated diimine ligands are magnetically equivalent. As a result, a single NH resonance in tc-[RuCl2(L)2] appeared at approximately δ 12.40. By contrast, the cc-isomer is unsymmetrical and a complex pattern of 1H NMR was observed in this case. Thus, there were two NH resonances observed in the range approximately δ 14.11–11.88. A semi-empirical extended Huckel MO calculations on a representative example showed strong metal–ligand overlap. A highly intense electronic transition that appeared in the visible range spectra of the complexes was assigned to a transition involving two molecular orbitals with considerable metal and ligand contributions. Both the isomers of the complex showed a high potential anodic response (0.8 V) due to the RuIII/RuII couple. The trivalent congeners [RuCl2(L)2]+ were generated in solution which showed characteristic rhombic EPR for the low spin d5 ions. The distortion parameters have been computed using the observed g values. The axial distortion (Δ) in each case is found to be stronger than the rhombic (V) distortion.

RUTHENIUM(III)-PROMOTED OXIDATIVE DIMERIZATION OF ANILINE TO N-PHENYL-1,2-PHENYLENEDIIMINE. DEFINITIVE PROOF FOR THE TEMPLATE REACTION

Two novel examples of ruthenium-promoted oxidative ortho-dimerization of aniline are described which demonstrate that the dimerization reaction proceeds via coordination of anilines to the metal ion.

Osmium(ii) complexes of N-aryl-1,2-arylene diimines formedviaortho-dimerization of ArNH2: synthesis,structure and redox properties

A family of ortho-arylene diimine chelates, [OsBr 2 L 2 ] (L = N-aryl-1,2-arylene diimine), which represent the first examples of osmium–quinonediimine complexes, are isolated from the reaction of [NH 4 ] 2 [OsBr 6 ] with aromatic amines, ArNH 2 .

Ruthenium- and osmium-promoted oxidation of aromatic amines. Some observations in the area of metal-diimines

Three reactions of aniline with Ru(acac)3, RuCl3·3H2O and (NH4)2[OsBr6] are reported. The isolated complexes are Ru(acac)2L, RuCl2(aniline)2L and OsBr2L2 (L=N-phenyl-1,2-phenylene diimine) respectively. In all the cases oxidation of aniline has occurred to result in diimine chelates. The products of the above reactions have been fully characterized and their X-ray structures are reported. The bond length trends within the chelate as well as the aromatic rings are consistent with the diimine character of the coordinated ligand. A qualitative pathway for the formation of L is suggested. A correlation between the metal oxidation levels in the starting compounds and the products with the number of ligand formation is noted.