Alok K. Deb

MONOVALENT COPPER COMPLEXES OF N-ARYL- PYRIDINE-2-ALDIMINE. SYNTHESIS, CHARACTERIZATION AND STRUCTURE

Abstract —A direct synthetic route, based on silver(I) assisted metal exchange reaction, to cationic bis-ligand complexes of copper(I) involving N-aryl-pyridine-2-aldimines (L, 1) has been studied. These complexes are obtained as their perchlorates, [Cu(L) 2 ]ClO 4 (2). They have been characterized with the help of spectroscopy and X-ray crystallography. The X-ray structure of [Cu(L 2 ) 2 ]ClO 4 , where L 2 is N-p-tolyl-pyridine-2-aldimine is reported. There are two crystallographically independent molecules in the asymmetric unit. The ligand L 2 coordinates in a bidentate manner providing a highly distorted tetrahedral geometry about copper. The complexes show highly resolved symmetrical 1 H NMR spectra. Intense MLCT absorptions are observed in the visible range. In methanol the CuL 2 2+ /CuL 2 + couple has E 1/2 ca, 0.35 V vs SCE at 298 K. The moderately high positive potential is brought about by the distortion in the geometry of CuL 2 2+ .

Isomeric complexes of ruthenium(II) with neutral heterocyclic schiff base ligands. High resolution proton resonance spectra of trans-cis isomeric pairs of RuX2L2 (L 2-arylpyridinecarboxaldimine, X Cl, Br) and comparison of their physical properties

Abstract The reaction of 2-arylpyridinecarboxaldimine [RH4C6NC(H)Py, L (1)] with hydrated RuX3 (X  Cl, Br) in boiling C2H5OH affords dark crystals of RuX2L2. Two geometrical isomers of the compound have been isolated and characterized by analytical and spectroscopic data. The trans isomer of RuCl2L2 shows a single sharp band for ν(RuCl), whereas two bands are observed for the corresponding cis isomer. The highresolution 1H NMR spectra of the isolated complexes are reported and completely assigned. All the complexes have multiple t2→π*(L) transitions in the visible region. Each of the complexes display a quasi-reversible oxidative response due to an RuIII/RuII couple in the range 0.25–0.40 V vs S.C.E. at a platinum working electrode. The formal potentials of this couple obey the Hammett relationship. The ligand-based irreversible oxidations are also briefly noted.

Isomeric dithiocyanate complexes of ruthenium(II), synthesis, characterization of all possible bond isomers of trans,cis-Ru(CNS)2L2 [L = 2-(arylazo)pyridine] and studies of isomerization

Abstract A series of isomeric new dithiocyanate ruthenium(II) complexes of the type trans,cis-Ru(CNS)2L2[L = 2-(arylazo)pyridine] have been synthesized by a stereoretentive substitution reaction from the known diaquo cationic complex trans,cis-[Ru(OH2)2L2]2+. All possible linkage isomers have been separated on a silica gel column and investigated for linkage isomerism. These isomers have been thoroughly characterized from physical properties, 1H NMR, IR and UV-vis spectroscopy. It has been shown that the most stable linkage isomer in this case is S,S bonded. Two (S,N and N,N) out of three isomers of trans,cis-Ru(CNS)2L2 are converted into the third (S,S) isomer on boiling in xylene. Similar transformations have also been observed in the solid state. Factors influencing the population of the various isomers are noted.

New, stable, chelated, tetracoordinated silver(I) complexes of the 2-(arylazo)pyridine ligand system : synthesis, characterization and assessment of bonding and structure

Abstract The 2-(arylazo)pyridines (L, 1) in methanol gave bis-chelated silver complexes, [AgL2]+ (2), as the crystalline perchlorate salts which were characterized by elemental analyses. The complexes are 1:1 electrolytes in methanol. In contrast to the copper analogue, there is only a small shift of v(NN) to low energy in the IR spectrum of [AgL2]+ as compared to that of uncoordinated L, indicating a negligible dπ—π*(L) interaction. The high resolution 1H NMR spectra of silver complexes with different substituted ligands (L1—L3) are reported. The complexes are quite stable and solutions in methanol and chloroform obey Beers law.

Reactions of primary aromatic amines with strongly electrophilic no coordinated to a ruthenium complex of 2-(phenylazo)pyridine

Abstract The diazotization of primary aromatic amines with a strongly electrophilic mononitrosyl complex, [Ru(NO)(NO 2 )L 2 ](ClO 4 ) 2 [L = 2-(phenylazo)pyridine], in acetonitrile and dichloromethane, is described. The reactions were studied by following the reaction sequence through the isolation of products at various stages of each reaction.

New ruthenium(II) complexes of α,α′-diimines. Synthesis, electrochemical and optical spectral properties of mononuclear complexes containing aryl(2-pyridylmethylene)amine and 2,2′-bipyridine ligands

The tris-chelated complexes, [RuLn(bipy)3 –n][ClO4]2·H2O [L = aryl(2-pyridylmethylene)amine, bipy = 2,2′-bipyridine, n= 0–3], have been prepared based on a direct and general route. For [RuL3]2+, the geometry has been assessed by 1H NMR spectroscopy. All the complexes show metal-to-ligand charge transfer (m.l.c.t.) transitions in the visible range at ca. 475 nm. Preliminary results of emission spectra are also described briefly. The metal oxidation as well as ligand reductions for the complexes have been studied electrochemically in acetonitrile using different working electrodes. It has been shown, for the mixed L–bipy complexes, that the reductions of co-ordinated L occur at comparatively lower negative potentials. The correlation between the electrochemical properties and vc.t.(absorption) is discussed.

Synthesis, characterization and high-resolution proton resonance spectra of [AgL2]ClO4 (L = 2-arylpyridinecar☐yaldimine) and their reactivities

The synthesis and characterization of bischelated silver(I) complexes of L(1) (L = 2-arylpyridinecar☐aldimine), [AgL2]ClO4 is reported. Solutions of the complexes are stable in methanol and chloroform, but unstable in acetonitrile. The chemical reactions of the silver complexes with chlorides of iron(III), cobalt(II) and nickel(II) have been examined. In all cases metal-exchange reactions take place to yield ML32+ [M = iron(II), cobalt(II) and nickel(II)]. These compounds have been characterized by comparison of their spectral data with those of authentic samples. The redox properties of the compounds are also briefly noted.

Oxidation reactions by the coordinated nitrosyl group

Abstract The oxidation reaction by the coordinated nitrosyl group in [Ru(NO)(NO2)(m-tap)2](ClO4)2 (1) (m-tap = m-tolylazopyridine) is described. Complex 1 brings about the oxidative coupling of N,N-dimethylaniline (DMA) to tetramethylbenzidine (TMB) and the oxidation of RuCl2(bpy)2 (bpy = 2,2′-bipyridin) to [RuCl2(bpy)2]+. These redox reactios have been studied voltametrically and the results have been analysed in terms of the electrophilicity of the coordinated NO+ in 1.

Synthesis, characterisation, and reactivity of new mononitrosyl complexes of ruthenium containing 2-(arylazo)pyridines: examples of strongly electrophilic nitrosyls

A high-yield synthetic route to ruthenium mononitrosyls of type [Ru(NO)(NO2)L2]2+(3)[L = 2-(arylazo)pyridine] from the dinitro precursor, [Ru(NO2)2L2](2) is described. Complexes (3) were isolated as crystalline perchlorate salts. In an alkaline medium, (3) regenerates (2). The electronic spectra of complexes (2) and (3) exhibit allowed metal-to-ligand charge-transfer transitions in the visible region, 400–550 nm. The nitrosyls absorb at high wavenumbers[ν(NO)ca. 1 950 cm–1] in the i.r. spectra. All the complexes are electroactive. Secondary oxidation of co-ordinated nitrite in (2) occurs after electrochemical metal oxidation. In the case of complexes (3), two successive one-electron reductions have been observed at relatively high positive potentials.

Oxidation of coordinated azomethine to amide. Synthetic and structural studies on a rhenium and a ruthenium system

The title reaction is exemplified by the high yield conversions 1→2 and 3→4 by H2O2, and the X-ray structures of 2 and 4 are reported; the species 1+ and 3+ afford 2 and 4 respectively when treated with water.