Govindan Prakash

Ruthenium(III) S-methylisothiosemicarbazone Schiff base complexes bearing PPh3/AsPh3 coligand: Synthesis, structure and biological investigations, including antioxidant, DNA and protein interaction, and in vitro anticancer activities

New Ru(III) isothiosemicarbazone complexes [RuCl(EPh3)L(1-4)] (E=P or As) were obtained from the reactions between [RuCl3(EPh3)3] and bis(salicylaldehyde)-S-methylisothiosemicarbazone (H2L(1-3))/bis(2-hydroxy-naphthaldehyde)-S-methylisothiosemicarbazone (H2L(4)) ligands. The new complexes were characterized by using elemental analyses and various spectral (UV-Vis, IR, (1)H NMR, FAB-Mass and EPR) methods. The redox properties of the complexes were studied by using cyclic voltammetric method. The new complexes were subjected to various biological investigations such as antioxidant assays involving DPPH radical, hydroxyl radical, nitric oxide radical and hydrogen peroxide, DNA/protein interaction studies and in vitro cytotoxic studies against human breast cancer cell line (MCF-7). New complexes showed excellent free radicals scavenging ability and could bind with DNA via intercalation. Protein binding studies using fluorescence spectroscopy showed that the new complexes could bind strongly with bovine serum albumin (BSA). Photo cleavage experiments using DNA of E-coli bacterium exhibited the DNA cleavage ability of the complexes. Further, the in vitro anticancer activity studies on the new complexes against MCF-7 cell line exhibited the ability of Ru(III) isothiosemicarbazone complexes to suppress the development of malignant neoplastic disease cells.

Ruthenium(II) complexes containing a phosphine-functionalized thiosemicarbazone ligand: synthesis, structures and catalytic C–N bond formation reactions via N-alkylation

A series of ruthenium(II) complexes incorporating a thiosemicarbazone chelate tethered with a diphenylphosphine pendant have been studied. Thus, [(PNS-Et)RuCl(CO)(PPh3)] (1), [N,S-(PNS-Et)RuH(CO)(PPh3)2] (2) and [(PNS-Et)RuCl(PPh3)] (3) were synthesized by reactions of various RuII precursors with 2-(2-(diphenylphosphino)benzylidene)-N-ethylthiosemicarbazone (PNS-Et). However, complexation of PNS-Et with an equimolar amount of [RuCl2(dmso)4] resulted in two different entities [(PNS-Et)RuCl(dmso)2] (4) and [(PNS-Et)2Ru] (5) with different structural features in a single reaction. All the RuII complexes have been characterized by analytical and various spectroscopic techniques. Compounds 1–5 were recrystallized, and the X-ray crystal structures have been reported for 1, 2 and 5. In the complexes 1 and 3–5 the ligand coordinated in a tridentate monobasic fashion by forming PNS five- and six-membered rings, whereas in 2, the ligand coordinated in a bidentate monobasic fashion by forming a strained NS four-membered ring. Furthermore, compounds 1–5 showed catalytic activity in N-alkylation of heteroaromatic amines. Notably, complexes 1–3 were found to be very efficient catalysts toward N-alkylation of a wide range of heterocyclic amines with alcohols. In the presence of a catalytic amount of 2 with 50 mol% of KOH, N1,C5-dialkylation of 4-phenylthiazol-2-amine has been investigated. Reaction of in situ generated aldehyde with amine yields the N1,C5-dialkylated products through the hydride ion transformation from alcohol. Complexes 1–3 also catalyzed a variety of coupling reactions of benzyl alcohols and sulfonamides, which were realized often with 99% isolated yields. Advantageously, only one equivalent of the primary alcohol was consumed in the process.

New ruthenium(II) carbonyl complexes bearing disulfide Schiff base ligands and their applications as catalyst for some organic transformations

Schiff base disulfide ligands (H2L(1-6)) were synthesized from the condensation of cystamine with salicylaldehyde(H2L(1)), 5-chlorosalicylaldehyde(H2L(2)), o-vanillin(H2L(3)), 2-hydroxyacetophenone(H2L(4)), 3-methyl-2-hydroxyacetophenone(H2L(5)), and 2-hydroxy-1-naphthaldehyde(H2L(6)). H2L(1-6) reacts with the ruthenium precursor complex [RuHCl(CO)(PPh3)3] in benzene giving rise to six new ruthenium(II) complexes of general formula [Ru(CO)L(1-6)]. Characterization of the new complexes was carried out by using elemental and spectral (IR, UV-Vis, NMR ((1)H and (13)C) and Mass) techniques. An octahedral geometry was assigned for all the complexes based on the spectral data obtained. The catalytic efficiency of the new complexes in aldehyde to amide conversion in the presence of NaHCO3, N-alkylation of aniline in the presence of t-BuOK, and transfer hydrogenation of ketones in the presence of iPrOH/KOH reactions were studied. Furthermore, the effect of solvents and catalyst/substrate ratio on the catalytic aldehyde to amide conversion were also discussed.

Ruthenium(II) carbonyl complexes bearing quinoline-based NNO tridentate ligands as catalyst for one-pot conversion of aldehydes to amides and o-allylation of phenols

Six new octahedral ruthenium(II) carbonyl complexes having the general molecular formula [RuCl(CO)(B)L(1-2)] (B = PPh3, AsPh3 or py; L(1-2) = quinoline based NNO ligand) were synthesized. The quinoline based ligands behave as monoanionic tridentate donor and coordinated to ruthenium via ketoenolate oxygen, azomethine nitrogen and quinoline nitrogen. The composition of the complexes has been established by elemental analysis and spectral methods (FT-IR, electronic, (1)H NMR, (13)C NMR, (31)P NMR and ESI-Mass). The complexes were used as efficient catalysts for one-pot conversion of various aldehydes to their corresponding primary amides in presence of NH2OH · HCl and NaHCO3. The effect of catalyst loading and reaction temperature on catalytic activity of the ruthenium(II) carbonyl complexes were also investigated. The synthesized complexes also possess good catalytic activity for the o-allylation of phenols in the presence of K2CO3 under mild conditions. The complexes afforded branched allyl aryl ethers according to a regioselective reaction.

Nickel(II) complexes containing ONS donor ligands: Synthesis, characterization, crystal structure and catalytic application towards C-C cross-coupling reactions

AbstractNickel(II) complexes containing thiosemicarbazone ligands [Ni(L)2] (1-3) (L = 9,10-phenanthrenequinonethiosemicarbazone (HL1), 9,10-phenanthrenequinone-N-methylthio semicarbazone (HL2) and 9, 10-phenanthrenequinone-N-phenylthiosemicarbazone (HL3)) have been synthesized and characterized by elemental analysis and spectroscopic (IR, UV-Vis, 1H, 13C-NMR and ESI mass) methods. The molecular structures of complexes 1 and 2 were identified by means of single-crystal X-ray diffraction analysis. The analysis revealed that the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative tridentate ONS fashion. The catalytic activity of complexes towards some C–C coupling reactions (viz., Kumada-Corriu, Suzuki-Miyaura and Sonogashira) has been examined. The complexes behave as efficient catalysts in the Kumada-Corriu and Sonogashira coupling reactions rather than Suzuki-Miyaura coupling. Graphical AbstractNickel(II) complexes bearing 9,10-phenanthrenequinone N-substituted thiosemicarbazone ligands were synthesized and characterized. The X-ray crystal structure of the complexes revealed a distorted octahedral geometry around the metal centre. These nickel complexes exhibited better catalytic activity in Kumada-Corriu and Sonogashira cross-coupling reactions than in Suzuki-Miyaura reaction.