Browsing by Author "Avadhesh K. Singh"

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Highly efficient and recyclable pre-catalysts based on mono- and dinuclear heteroleptic Cu(I) dithio- PPh3 complexes to produce variety of glycoconjugate triazoles
(Elsevier B.V., 2019) Avadhesh K. Singh; Chote Lal Yadav; Kunj Bihari Mishra; Santosh K. Singh; Ajit N. Gupta; Vinod Kumar Tiwari; Michael G.B. Drew; Nanhai Singh
Highly efficient and reusable pre-formed mono- and dinuclear heteroleptic copper(I) dithiocarbamate and dithiocarbimate complex based catalysts, [Cu(PPh3)2(L)] and [Cu2(PPh3)4(L)] (L = N-(4-methylpyridyl)-N-(3-methylpyridyl)dithiocarbamate− L1 1, N-methylfuryl-N-methylthiophenedithiocarbamate- L2 2; 4-chlorobenzenesulfonyl dithiocarbimate2- L3 3, 4-bromobenzenesulfonyldithiocarbimate2- L4 4) have been utilized in the cycloaddition reactions of azide and alkyne to form a variety of glycoconjugate triazoles in Click chemistry. These new pre-catalysts have been characterized by elemental (C, H, N) analysis, IR, UV–vis., 1H, 13C{1H}, and 31P{1H} NMR spectroscopy and their structures have been revealed by X-ray crystallography. In the structures of (1,2)/(3,4) the copper atoms are situated within a four coordinate (P2S2)/(P2NS) distorted tetrahedral geometry. Notably in the dinuclear complexes 3 and 4, the dithiocarbimate ligands are bonded in a S, S- chelating mode to one copper atom and simultaneously bridge the other copper centre via N, S- donor atoms. 1-4 are strongly luminescent in CH2Cl2 solution at room temperature. © 2019 Elsevier B.V.
Synthesis, crystal structures and conducting properties of heteroleptic nickel(II) 1,1-dithiolate-bpy/dppe ligand complexes
(Elsevier Ltd, 2015) Ajit N. Gupta; Vinod Kumar; Vikram Singh; Krishna K. Manar; Avadhesh K. Singh; Michael G.B. Drew; Nanhai Singh
New heteroleptic complexes, [Ni(LL′)] (L = 2-(methylene-1,1′-dithiolato)-5,5′-dimethylcyclohexane-1,3-dione (L1), L′ = 2,2′-bipyridyl (bpy) 1; L = 2-(methylene-1,1′-dithiolato)-1,3-indandione (L2), L′ = 1,2-bis(diphenylphosphino)ethane (dppe) 2) have been synthesized and characterized by elemental analysis, IR, NMR and UV-Vis spectroscopy, and their structures have been determined crystallographically. In the two structures, the Ni atom lies at the centre of a distorted square plane. In 1, the ligand L1 is uniquely bonded to the Ni atom in an adjacent molecule in a μ2, κ2 S,S-chelating-bridging manner, forming a weak dimer with a Ni...S distance of 2.96 Å, which is shorter than the sum of the van der Waal's radii of the Ni and S atoms. In 2 the steric restrictions of the bulky dppe ligand hindered any dimerization, but result in the formation of a rare intramolecular C-H...Ni anagostic interaction between the ortho hydrogen atom of the phenyl ring and the nickel centre, which has been assessed by theoretical calculations. The supramolecular structures of 1 and 2 are sustained by π(chelate)...π(bpy), C-H...O, C-H...π(chelate) and C-H...π(Ar) interactions. The two compounds are weakly conducting (σrt = 10-7-10-5 S cm-1), but show semiconducting behavior in the 303-363 K temperature range. © 2015 Elsevier Ltd. All rights reserved.