• Sreebrata Goswami

      Articles written in Journal of Chemical Sciences

    • Use of silver (I) complexes in synthesis. A generalised approach to the synthesis of some transition metal complexes

      Subrata Choudhury Alok K Deb Wancydora Kharmawphlang Sreebrata Goswami

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      Efficient, new and direct synthetic routes for the syntheses of some transition metal complexes N,N donors, based on the reactions of metal chloride salts and silver(I) complexes of the corresponding ligands, have been described. It has been shown that synthesis of mixed ligand complexes of desired composition may easily be made by following thesetrans metallation reaction routes. Comparison of these routes with the reported synthetic methods have been discussed. Possible applications of these synthetic strategies for the synthesis of polynuclear species have been briefly noted.

    • Ruthenium(III) complexes of β-ketoamines. Examples of unusually low Ru(IV)/Ru(III) reduction potentials

      Subrata Choudhury Sreebrata Goswami

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    • Synthesis, chemical reactions and redox properties of ruthenium complexes of a tetradentatebis chelating ligand, 2,2′-azobis(pyridine)

      Partha Majumdar Alok K Deb Sreebrata Goswami

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      The use of silver (I) assisted metal exchange reaction for the synthesis of mononuclear ruthenium (II) complexes of a tetradentate bridging ligand, 2,2′-azobis(pyridine) (L1) is elaborated. This route has been successfully employed for the direct synthesis of RuCl2(L1)2 (2); [Ru(L1)3](ClO4)2·H2O (3) from RuCl3·3H2O and for the mixed ligandtris chelates of general composition [Ru(L1)n(L)3−n]2+ (n=0–3;L=neutral N,N donors: 2-(phenylazo)pyridine (L2), 2,2′-bipyridine(L3)). The preparation of [Ru(OH2)2(L1)2]2+ (7) from 2 is also described. The diaquo complex,7, is chemically reactive and undergoes anation, solvolysis and substitution reactions instantaneously with different nucleophiles. All the reactions, described above, occur smoothly and the yields of the products are high. The composition and identities of the complexes are established from their elemental analyses and spectral data. The redox properties of the compounds have been examined. Metal oxidation responses occur at very high positive potentials. Successive reductive responses occur on the negative of the SCE.

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

      Kedar N Mitra Sreebrata Goswami

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      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.

    • Metal mediated amination of aromatic rings following carbon-nitrogen bond formation and the coordination chemistry thereof

      Amrita Saha Amit K Ghosh Partha Majumdar Sreebrata Goswami

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

      Kunal K Kamar Amrita Saha Sreebrata Goswami

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      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.

    • Synthesis, structure, redox and spectra of green iridium complexes of tridentate azo-aromatic ligands

      Manashi Panda Chayan Das Chen-Hsiung Hung Sreebrata Goswami

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      Reactions of IrCl$_3 \cdot x$H2O with the ligands, 2-[(phenylamino)phenylazo]pyridine (HL$^{1a}$) and 2-[(𝑝-tolylamino)phenylazo]pyridine (HL$^{1b}$) produce [Ir(L1)2]Cl (L1 = L$^{1a}$, [1]Cl and L1 = L$^{1b}$, [2]Cl) along with many unidentified products. The iridium complexes have been characterized by various techniques such as X-ray crystallography, mass spectrometry, 1H and 13C NMR, cyclic voltammetry and absorption studies. The complex [1]ClO4 crystallises in triclinic space group. The crystallographic data have been determined. Notably, the Ir-N (azo) lengths are short (av. 1.9875(4) Å) as compared to the remaining four Ir-N lengths (av. 2.052(5) Å). There is significant degree of ligand backbone conjugation in the coordinated ligands, which result in shortening of the C-N lengths on the other side of the middle phenyl ring and also in lengthening of the diazo (N=N) lengths. The complexes display multiple low energy transitions ranging between 1010 and 450 nm. These are electro active and show three reversible redox responses in the potential range, +1.5 V to -1.5 V. The cathodic potential responses are ascribed as ligand reductions, while the redox process at the anodic potential occurs at a mixed metal-ligand (HOMO) orbital.

    • Identification of a (H2O)8 cluster in a supramolecular host of a charge transfer platinum(II) complex

      Sutanuva Mandal Ipsita Chatterjee Alfonso Castiñeirs Sreebrata Goswami

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      The chemical reaction of PtII(L1)Cl2 [L1 = 2-(phenylazo)pyridine] with a bidentate N,S-donor atom ligand, 2-phenylthioaniline, (HL2) in alkaline acetonitrile yielded a mixed ligand donor acceptor complex, [PtII(L1)(L2)−]Cl, [1]Cl. The complex has been characterized by using a host of physical methods: X-ray crystallography, nuclear magnetic resonance, cyclic voltammetry, absorption spectroscopy, electron paramagnetic resonance. The complex showed intense interligand charge transfer (ILCT) transition in the long wavelength region of UV-vis spectrum at 785 nm. The single-crystal X-ray structure of complex, [1]Cl·2.6H2O is reported. The cationic complex upon crystallization from aqueous methanol solvent produces an assembly of three dimensional (H2O)8 guest moiety within the host lattice of reference Pt-complex. The water assembly showed a unique type of aggregation of two trigonal pyramids hydrogen bonded with three chloride anions. The complex displayed two reversible responses at −0.34 and −1.05 V along with one irreversible anodic response at 0.91 V versus Ag/AgCl reference electrode. The redox processes are characterized by examination of EPR spectra of the electrogenerated complexes.

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