Kunal K. Kamar

Ruthenium complexes of quinone related N-aryl-1,2-diimines. Metal mediated synthesis, X-ray structure and chemical reaction

A family of ruthenium N-aryl-1,2-diiminoarene chelate complexes, [RuCl2(bpy)(diim)], 1 (bpy=2,2′-bipyridine, diim=N-aryl-1,2-diiminoarene) were isolated from the reaction of [RuCl3(bpy)] and a primary aromatic amine (ArNH2) in the presence of aerial oxygen. The diim ligand was formed in situ due to oxidative dimerisation of ArNH2. The metal complex, in this reaction, acts as a mediator. The dichloro complexes were characterized based on their physicochemical data. The X-ray structure of one member of the family was determined and the results used to authenticate the formation of the product from an unusual oxidative fusion of aromatic monoamines. The X-ray structure of 1c (substituent R on the aromatic ring=Cl) revealed a cis geometry with respect to two coordinated chlorides. The bond length trends within the chelate as well as the aromatic rings are consistent with a diimine oxidation state of the ligand bound to ruthenium in its bivalent oxidation state. These complexes showed multiple transitions in the near-IR and visible regions. The highly intense transition at around 540 nm has been assigned to a transition involving two heavily mixed metal–ligand orbitals. The ruthenium(III)/ruthenium(II) couple for the dihalo complexes appeared at a high anodic potential (range 0.50 to 0.90 V), which for differently substituted compounds depend on the Hammett ∑σp parameters of the substitution on the diim ligand. The syntheses and characterization of a few heteroleptic tris-chelates, [Ru(bpy)(diim)L](ClO4)2·nH2O (L=a bidentate N,N-donor), involving the reaction of 1 with two moles of the silver reagent, [AgL2](ClO4), are reported. The tris-chelates showed intense charge transfer in their electronic spectra and multiple cathodic voltammetric responses, which have been assigned as reductions of coordinated ligands.

Unusual binding mode of the biimidazolate bridgingligand in two novel heteropolynuclear complexes with anM2Ag2 [M = Ru(II) or Os(II)]core

Two novel examples of heteronuclear tetrametallic M2Ag2 (M = Ru, Os) complexes are described which show strong argentophilic interactions.

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

This presentation reports some novel examples of organic ring amination reactions via metal mediation. The organic transformations are highly regioselective and can be controlled by the proper selection of the mediator complex. The two isomeric organic ligands viz. HL1 and HL2 were isolated in their pure states by the removal of the metal ions. These were fully characterized. The ligand HL1 has lowpKa, 8.5. Upon deprotonation, it behaves as a potentialbis chelating N,N,N-donors. The coordination chemistry of the HL1 ligand involving some 3d-metal ions is described. Two unusual low-spin complexes of manganese(II) and iron(III) are reported. The ferric complex displayed a rhombic EPR while, the corresponding manganese compound showed a complex pattern due to hyperfine coupling. All the complexes displayed large number of redox responses. A brief mention about the future projection of this work is noted.