Browsing by Author "Mahendra Yadav"

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Coordination polymers and monomers based on new aminocarboxylate ligands: A cadmium(II) polymer containing dimeric aqua-bridged cadmium complex governed by polymeric chain
(Elsevier S.A., 2011) Rampal Pandey; Mahendra Yadav; Prashant Kumar; Pei-Zhou Li; Sanjay Kumar Singh; Qiang Xu; Daya Shankar Pandey
The synthesis and characterization of novel coordination polymers [Co(HCCB)(H2O)2]n (1), [Zn(HCCB)(H 2O)2]n (2), {[Cd(HCCB)2]·0. 5[Cd(μ-H2O)(H2O)4]2}n (3) and [Cu(HCCB)(H2O)2]n (4) based on 3-(carboxymethylamino)-4-chlorobenzoic acid (H3CCB) and mononuclear complexes [Cu(HBCCB)(H2O)]·H2O (5), [Co(HBCCB)(H2O)]·H2O (6), [Zn(HBCCB)(H 2O)] (7) and [Cd(HBCCB)(H2O)] (8) containing 3-bis(carboxymethylamino)-4-chlorobenzoic acid (H3BCCB) have been described. The compounds under investigation have been characterized by elemental analyses, spectral studies and structures of 1-3 and 5 determined crystallographically. Structural data of 1 and 2 revealed that the deprotonated HCCB2- bridges metal centers leading to a double stranded 1D chain. On the other hand, the HCCB2- coordinated thorough carboxylate oxygen and amino nitrogen in 3 to afford a 1D chain whose charge neutrality is maintained by inclusion of aqua-bridged dimer [{Cd(μ-H2O)(H 2O)4}2]4+. Strong Cu⋯Cl interaction (2.754 ) in 5 imposes a coordination geometry that is half-way between the square planar and square pyramidal. The H3CCB, H 3BCCB and 1-3 and 5 are fluorescent at rt. Thermal studies (TG and DSC) on 1-3 suggested higher stability of 2 relative to 1 and 3 [ΔH f (kcal/mol), ΔSf = 152.17, 0.60, 1; 195.56: 0.86, 2; 69.33:0.36, 3]. © 2011 Elsevier B.V. All rights reserved.
Design and synthesis of fluorescent 6-aryl[1,2-c]quinazolines serving as selective and sensitive on-off chemosensor for Hg 2+ in aqueous media
(2012) Rampal Pandey; Mahendra Yadav; Mohammad Shahid; Arvind Misra; Daya Shankar Pandey
Three fluorescent quinazolines thiophen-2-yl-5,6-dihydrobenzo-[4,5] imidazo[1,2-c]quinazoline (1), pyridin-3-yl-5,6-dihydrobenzo-[4,5]imidazo-[1,2- c]quinazoline (2) and phenyl-5,5′,6,6′-dihydrobenzo-[4,4′,5, 5′]imidazo-[1.1′,2-c,2′-c]quinazoline (3) have been synthesized. Structures of 1 and 3 have been authenticated crystallographically. Quinazolines 1-3 exhibit highly selective on-off switching for Hg 2+ ions. The fluorescence intensity displayed a linear relationship with respect to Hg 2+ concentration (0.1-1.0 μM; R 2 = 0.99) with detection limit of 2.0 × 10 -7 M. © 2012 Published by Elsevier Ltd.
Extended molecular networks based on Zn and Cd imparting N-substituted imidazole
(Elsevier S.A., 2010) Ashish Kumar Singh; Mahendra Yadav; Sanjay Kumar Singh; Sailaja Sunkari; Daya Shankar Pandey
Synthesis of complexes with the formulations [M(CPI)2Cl2] (M = Zn, 1; M = Cd, 4) and [M(CPI)6](X)2 (M = Zn, X = NO3-, 2; X = ClO4-, 3; M = Cd, X = NO3-, 5; X = ClO4-, 6) have been achieved from the reactions of MCl2, M(NO3)2·xH2O and M(ClO4)2·xH2O (M = Zn, Cd) with 1-(4-cyanophenyl)-imidazole (CPI). Complexes 1-6 have been characterized by elemental analyses and spectral studies (IR, 1H, 13C NMR, electronic absorption and emission). Molecular structures of 1, 2, 3 and 6 have been determined crystallographically. Weak interaction studies on the complexes revealed presence of various interesting motifs resulting from C-H···N, C-H···Cl and π-π stacking interactions. The complexes under study exhibit strong luminescence at ∼450 nm in DMSO at room temperature. © 2009 Elsevier B.V. All rights reserved.
First examples of heteroleptic dipyrrin/η5- pentamethylcyclopentadienyl rhodium/iridium(III) complexes and their catalytic activity
(2009) Mahendra Yadav; Ashish Kumar Singh; Daya Shankar Pandey
Heteroleptic pentamethylcyclopentadienyl rhodium/iridium(III) complexes imparting dipyrrins as co-ligands with the general formulations [(η5-C5Me5)MCl(L)] [(M = Rh(III) or Ir(III); L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl) dipyrromethene, ndpm; and 5-(4-benzy-loxyphenyl)dipyrromethene, bdpm] have been synthesized. Reactivity of the complexes [(η5-C 5Me5)MCl(L)] (M = Rh(III), Ir(III); L = ndpm and cydpm) with various species, viz., sodium azide (NaN3), ammonium thiocyanate (NH4SCN), triphenylphosphine (PPh.3), 4,4′-bipyridine (bpy), and bis(diphenylphosphino)hexane (dpph), has been examined. Resulting complexes have been characterized by elemental analyses and spectral and electrochemical studies. Molecular structures of the representative complexes [(η5-C5Me5)RhCl(cydpm)], [(η5-C5Me5)RhCl(ndpm)], [(η5-C5Me5)Rh-(PPh3)(cydpm)] SO3CF3, and [(η5-C5Me 5)Ir(PPh3)(ndpm)]SO3CF3 have been determined crystal-lographically. The complexes [(η5-C 5Me5)MCl(L)] [(M = Rh(III) or Ir(III) and L = cydpm, ndpm, or bdpm) effectively catalyze reduction of terephthalaldehyde to 4-hydroxymethybenzaldehyde in the presence of HCOOH/CH3COONa in water under aerobic conditions. Among these complexes the rhodium complex [(η5-C5Me5)RhCl(ndpm)] is most effective in this regard. © 2009 American Chemical Society.
First examples of homo-/heteroleptic bi-/tri-nuclear complexes containing 5-ferrocenyldipyrromethene
(2009) Mahendra Yadav; Prashant Kumar; Ashish Kumar Singh; Joan Ribas; Daya Shankar Pandey
The first examples of homo- and heteroleptic complexes containing 5-ferrocenyldipyrromethene (fcdpm) [Cu(fcdpm)2] (1) [Cu(fcdpm)(acac)] (2), [Ni(fcdpm)(acac)] (3) and [Zn(fcdpm)2] (4) (acac = acetylacetonato) are described. Formation of the asymmetric metal complexes has been followed by electronic absorption and infrared spectroscopy. The complexes have been characterised by elemental analyses and spectral studies. Structures of [Cu(fcdpm)2] (1), [Cu(fcdpm)(acac)] (2) and [Ni(fcdpm)(acac)] (3) have been determined crystallographically. Structural data revealed that the metal centre in the copper complexes [Cu(fcdpm)2] (1), [Cu(fcdpm)(acac)] (2) and the nickel complex [Ni(fcdpm)(acac)] (3) adopts a distorted square planar geometry. © The Royal Society of Chemistry 2009.
Half-sandwich ruthenium, rhodium and iridium complexes containing dipyridyl amine based ligands
(2010) Daya Shankar Pandey; Ashish Kumar Singh; Mahendra Yadav; Rampal Pandey; Prashant Kumar
Compounds derived from the reactions of dimeric arene ruthenium [{(η6-arene)Ru(μ-Cl)Cl}2] (arene = benzene and p-cymene) and structurally analogous rhodium and iridium complexes [{(η5-C5Me5)M(μ-Cl)Cl}2] (M = Rh or Ir) with 2-chloro-4,6-(di-2-pyridylamino)-1,3,5-triazine (cddt) and 2,4,6-tris(di-2-pyridylamino)-1,3,5-triazine (tdat) are reported. Compounds under investigation have been characterized by elemental analyses, NMR ( 1H and 13C), electronic absorption, emission spectral and electrochemical studies. Structures of the dinuclear compounds [{(η6-C10H14)RuCl}2(cddt)] (PF6)2, [{(η5-C5Me 5)RhCl}2(cddt)]Cl2·6H2O and trinuclear compound [{(η6-C6H6)RuCl} 3(tdat)]Cl3·4H2O have been determined crystallographically. Among cddt containing compounds the {(η6- C10H14)RuCl}- units in [{(η6-C 10H14)RuCl}2(cddt)](PF6) 2 are anti, while {(η5-C5Me 5)RhCl}- in the rhodium compound [{(η5-C 5Me5)RhCl}2(cddt)]Cl2·6H 2O are syn with respect to triazine ring. Cyclic voltammetric studies on the compounds suggested lack of communication between the metal centres. Furthermore, although tdat is luminescent at room temperature compounds under investigation containing this ligand are non-luminescent in acetonitrile. Compounds derived from the reactions of dimeric arene ruthenium [{(η6-arene)Ru(μ-Cl)Cl}2] (arene = benzene and p-cymene) and structurally analogous rhodium and iridium complexes [{(η5-C5Me5)M(μ-Cl)Cl}2] (M = Rh or Ir) with 2-chloro-4,6-(di-2-pyridylamino)-1,3,5-triazine (cddt) and 2,4,6-tris(di-2-pyridylamino)-1,3,5-triazine (tdat) are described. Compounds under study have been fully characterized by analytical, spectral and electrochemical studies and structures of [{(η6-C 10H14)RuCl}2(cddt)](PF6) 2, [{(η5-C5Me5)RhCl} 2(cddt)]Cl2·6H2O, and [{(η6-C6H6)RuCl}3(tdat)]Cl 3·4H2O have been authenticated crystallographically. © 2010 Elsevier B.V. All rights reserved.
Heteroleptic arene ruthenium complexes based on meso-substituted dipyrrins: Synthesis, structure, reactivity, and electrochemical studies
(2009) Mahendra Yadav; Ashish Kumar Singh; Biswajit Maiti; Daya Shankar Pandey
First examples of heteroleptic arene ruthenium complexes containing dipyrrin ligands with the general formulations [(η6-arene)RuCI(L) ] [(arene = C6H6, C10H14; L = 5-(4-cyanophenyl)-dipyrromethene, cydpm; 5-(4-nitrophenyl)-dipyrromethene, ndpm and 5-(4-benzyloxyphenyl)-dipyrromethene, bdpm] have been synthesized. The complexes [η6 -C10H14)RuCI(L)] (L = ndpm and cydpm) reacted with NaN3 and NH4SCN to afford neutral mononuclear complexes [(η6-C10H14)Ru(N 3)(L)] and [η6 -C10H14)Ru(SCN) (L)]. Their reactions with EPh3 (E = P, As) and exobidentate ditopic P-P and N-N donor ligands, namely, bis-(diphenylphosphino)methane (dppm) and 4,4′-bipyridine (bpy) in the presence of AgSO3CF3 afforded cationic mono- and binuclear complexes [(η6 -C 10-H14)Ru(L)(EPh3)]SO3CF 3, [{(η6-C10H14)Ru(L)} 2(μ-dppm)](SO3CF3)2, and [{(η6-C10H14)Ru(L)}2(μ-bpy)] (S03-CF3)2, respectively. The reaction products have been characterized by analytical and spectral studies. Molecular structures of the representative complexes [η6-C 10H14)RuCI(cydpm)], [(η6-C 6H6)RuCI(cydpm)], [η6-C10H 14)RuCI-(ndpm)], [(η6-C10H 14)Ru(N3)(ndpm)], and [η6-C 10H14)Ru(PPh3)(ndpm)]SO3CF 3 have been determined crystal-lographically. Redox behavior of the complexes has been investigated by electrochemical studies. Emission spectral studies at room temperature suggested that the complexes under study are non-emissive. © 2009 American Chemical Society.
Heteroleptic half-sandwich Ru(II), Rh(III) and Ir(III) complexes based on 5-ferrocenyldipyrromethene
(2011) Mahendra Yadav; Ashish Kumar Singh; Daya Shankar Pandey
The synthesis and characterization of heteroleptic complexes with the formulations [(η6-arene)RuCl(fcdpm)] (η6-arene = C6H6, C10H14) and [(η5-C5Me5)MCl(fcdpm)] (M = Rh, Ir; fcdpm = 5-ferrocenyldipyrromethene) have been reported. All the complexes have been characterized by elemental analyses, IR, 1H NMR and electronic spectral studies. Structures of [(η6-C6H 6)RuCl(fcdpm)] and [(η6-C10H 14)RuCl(fcdpm)] have been determined crystallographically. Chelating monoanionic linkage of fcdpm to the respective metal centres has been supported by spectral and structural studies. Further, reactivity of the representative complex [(η6-C10H14)RuCl(fcdpm)] with ammonium thiocyanate (NH4SCN) and triphenylphosphine (PPh 3) have been examined. © 2010 Elsevier Ltd. All rights reserved.
Heteroleptic rhodium complexes containing both the dipyrrin/cyclooctadiene ligands and application of [(η4-C8H12)Rh(4-pyrdpm)] in the construction of homo-/hetero-bimetallic complexes
(Elsevier Ltd, 2010) Mahendra Yadav; Prashant Kumar; Daya Shankar Pandey
Heteroleptic rhodium(I) complexes with the general formulations [(η4-C8H12)Rh(L)] [η4-C8H12 = 1,5-cyclooctadiene; L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl)dipyrromethene, ndpm; and 5-(4-benzyloxyphenyl)dipyrromethene, bdpm; 5-(4-pyridyl)dipyrromethene, 4-pyrdpm; 5-(3-pyridyl)dipyrromethene, 3-pyrdpm] have been synthesized. The complex [(η4-C8H12)Rh(4-pyrdpm)] have been used as a synthon in the construction of homo-bimetallic complex [(η4-C8H12)Rh(μ-4-pyrdpm)Rh(η5-C5Me5)Cl2] and hetero-bimetallic complexes [(η4-C8H12)Rh(μ-4-pyrdpm)Ir(η5-C5Me5)Cl2], [(η4-C8H12)Rh(μ-4-pyrdpm)Ru(η6-C10H14)Cl2] and [(η4-C8H12)Rh(μ-4-pyrdpm)Ru(η6-C6H6)Cl2]. Resulting complexes have been characterized by elemental analyses and spectral studies. Molecular structures of the representative mononuclear complexes [(η4-C8H12)Rh(ndpm)] and [(η4-C8H12)Rh(4-pyrdpm)] have been authenticated crystallographically. © 2009 Elsevier Ltd. All rights reserved.
Luminescent N,O-chelated chroman-BF2 complexes: Structural variants of BODIPY
(2013) Roop Shikha Singh; Mahendra Yadav; Rakesh Kumar Gupta; Rampal Pandey; Daya Shankar Pandey
The synthesis and characterization of 5-(chromen-4-one)-dipyrromethane (1), 5-(6-methyl-chromen-4-one)-dipyrromethane (2), 5-(6-isopropyl-chromen-4-one)- dipyrromethane (3) and the respective chromans, 7-[2-pyrrolo]-pyrrole[1,2-a]12H pyrrolino[2,3-b]chroman-4-one (4), 4-methyl-7-[2-pyrrolo]-pyrrole[1,2-a]12H pyrrolino[2,3-b]-chroman-4-one (5) and 4-isopropyl-7-[2-pyrrolo]-pyrrole[1,2-a] 12H pyrrolino[2,3-b]-chroman-4-one (6) have been described. Chroman derivatives 4-6 have been used in the synthesis of highly stable, fluorescent, borondifluoride complexes (7-9). All the compounds have been fully characterised by various physicochemical techniques viz., elemental analyses, IR, HRMS, NMR (1H, 13C), electronic absorption, emission (solution and solid state), electrochemical and thermal studies. Crystal structures of dipyrromethanes 1 and 2, chroman derivative 6 and boron complexes 7-9 have been determined by X-ray single crystal analyses. Structural studies revealed that the formation of 4-6 takes place by DDQ mediated C-N coupling. The higher stability of 4-6 relative to their respective dipyrrins has been supported by theoretical studies. © The Royal Society of Chemistry 2013.
Metabolites Profiling, Bioactivity Assessment and Extracellular Enzymes Estimation of Pestalotiopsis sp. L12, an Endophytic Fungus Recovered from Saraca asoca (Roxb.) Willd. Leaves
(Pleiades Publishing, 2025) Jay Hind Nishad; Shubham Vishwakarma; Anil Kumar Singh; Mahendra Yadav; Rajnish Bharti; Ravindra Nath Kharwar
Abstract: The medicinal plant Saraca asoca harbors an endophytic fungal strain, which was identified as Pestalotiopsis sp. L12 by morphological and molecular analyses. It exhibited maximum amylase and cellulase production at 28°C after 72 h, releasing 41.66 µg of maltose and 35.66 µg of glucose. The crude extracts of isolate L12 showed antibacterial activity against such important pathogens as K. pneumoniae, S. aureus, and E. coli in addition to antioxidant properties. The effective concentration (EC50) of the crude extract for antioxidant activity against ABTS+ radical was 64 µg/mL. Furthermore, the GC-MS and HPLC-ESI-MS/MS analyses of the crude extracts identified six and seven compounds, respectively. Notably, one of the compounds, 6,9-dimethyltetradecan, is known for its antibacterial and antioxidant properties. Oleic acid and theophylline identified through mass fragmentation in HPLC-ESI-MS/MS analysis have also been well-recognized for antibacterial and antioxidant activities. © Pleiades Publishing, Ltd. 2025.
Novel structures based on 1-(4-cyanophenyl)-imidazole resulting from weak bonding interactions
(2009) Ashish Kumar Singh; Mahendra Yadav; Prashant Kumar; Sanjay Kumar Singh; Sailaja Sunkari; Daya Shankar Pandey
Mono-nuclear complexes [M(CPI)6](X)2 (M = Co, X = NO3- 1; M = Ni, X = NO3- 2; M = Cu, X = ClO4- 3) and [Cu(CPI)4(H2O)2](NO3)2 4, based on novel bridging ligand 1-(4-cyanophenyl)-imidazole (CPI) are reported. The complexes have been characterized by elemental analyses, spectral studies and their molecular structures have been authenticated by single crystal X-ray diffraction analyses. In molecular species 1-3 metal centers are coordinated octahedrally by six CPI ligands wherein cyanophenyl rings of six ligands about the complex cations are involved in face-to-face π-π interaction with six co-planar molecules to afford unprecedented 2D sheet. Along 'c'-axis it gives a beautiful rim like motif. In complex 4, coordination about metal center Cu is distorted octahedral with four CPI ligands in the equatorial position and two water molecules occupying axial positions. In this complex hydrogen bonding interactions between the coordinated water molecules and nitrate anions results in a 1D straight chain along 'a'-axis and 2D sheets having hexagonal cavity filled by nitrate ions. The complexes upon excitation at 275-285 nm exhibit luminescences with emission maxima centered at 438-445 nm attributable to the ligand CPI at room temperature. © 2009 Elsevier B.V. All rights reserved.
Synthesis and characterization of 3D metal complexes based on 1-(4-nitrophenyl)imidazole
(2011) Ashish Kumar Singh; Mahendra Yadav; Daya Shankar Pandey
Synthesis and characterization of complexes with formulations [M(nopi) 2Cl2] (M= Co, 1; Ni, 3; Cu, 6; Zn, 9), [M(nopi) 9](X)2 (X- = NO3-, M = Co, 2; Ni, 4; Zn, 10; X- = ClO4-, M = Ni, 5; Cu, 8; Zn, 11) and [Cu(nopi)4(NO3)2] (7) imparting 1-(4-nitrophenyl)imidazole (nopi) have been described. The complexes have been characterized by elemental analyses and spectral (IR, 1HNMR, electronic absorption and emission) studies. Molecular structures of 7 and 9 have been determined crystallographically. Weak interaction studies on 7 and 9 revealed the presence of various interesting motifs resulting from C-H⋯N, C-H⋯Cl, and π-π stacking interactions. Temperature-dependent (313-373 K) pressed pellet conductivity and activation energy calculations from the plot of ln σ vs. 1/T suggested semiconducting behavior of 2, 6, and 7. © 2011 The Chemical Society of Japan.
Synthesis and characterization of complexes imparting N-pyridyl bonded meso-pyridyl substituted dipyrromethanes
(2010) Mahendra Yadav; Ashish Kumar Singh; Rampal Pandey; Daya Shankar Pandey
The meso-pyridyl substituted dipyrromethane ligands 5-(4-pyridyl)dipyrromethane (4-dpmane) and 5-(3-pyridyl)dipyrromethane (3-dpmane) have been employed in the synthesis of a series of complexes with the general formulations [(η6-arene)RuCl2(L)] (η6-arene = C6H6, C10H14) and [(η5-C5Me5)MCl2(L)] (M = Rh, Ir). The reaction products have been characterized by microanalyses and spectral studies and molecular structures of the complexes [(η6-C10H14)RuCl2(4-dpmane)] and [(η5-C5Me5)IrCl2(3-dpmane)] have been determined crystallographically. For comparative studies, geometrical optimization have been performed on the complex [(η5-C5Me5)IrCl2(4-dpmane)] using exchange correlation functional B3LYP. Optimized bond length and angles are in good agreement with the structural data of the complex [(η5-C5Me5)IrCl2(3-dpmane)]. The complexes [(η6-C10H14)RuCl2(3-dpmane)], [(η5-C5Me5)RhCl2(3-dpmane)] and [(η5-C5Me5)IrCl2(3-dpmane)] have been employed as a transfer hydrogenation catalyst in the reduction of aldehydes. It was observed that the rhodium and iridium complexes mentioned above are more effective in this regard in comparison to the ruthenium complex. © 2010 Elsevier B.V. All rights reserved.
Synthesis and characterization of Ru(IV) and Rh(I) complexes containing phenylimidazole ligands
(2010) Daya Shankar Pandey; Rakesh Kumar Gupta; Ashish Kumar Singh; Mahendra Yadav; Prashant Kumar; Sanjay Kumar Singh; Peizhou Li; Qiang Xu
The reactions of chloro-bridged dimeric complexes [{(η3; η3-C10H16)Ru(μ-Cl)Cl}2] and [{(η4-C8H12)RhCl}2] with 1-(4-cyanophenyl)imidazole (CPI), 1-(4-nitrophenyl)imidazole (NOPI), 1-(4-formylphenyl)imidazole (FPI) and 1-(4-hydroxy-phenyl)imidazole (HPI) have been investigated. These reactions afforded complexes with the general formulations [(η3;η3-C10H 16)RuCl2(L)] (L = CPI, 1; NOPI, 2; FPI, 3; HPI, 4) and [(η4-C8H12)RhCl(L)] (L = CPI, 5; NOPI, 6; FPI, 7; HPI, 8). Resulting complexes have been characterized by analytical and spectral (IR, 1H and 13C NMR, UV-Vis) studies. Crystal structures of 2, 5 and 6 have been determined by single crystal X-ray diffraction analyses. Structural studies on the complexes 2, 5 and 6 revealed the presence of extensive inter- and intra-molecular C-H⋯X (X = O and Cl) and C-H⋯π interactions. Theoretical studies have been performed to authenticate the structures and NBO calculations to determine electronic properties of the complexes. Complexes of the general formulations [(h 3;h3-C10H16)RuCl2(L)] (L = CPI, 1; NOPI, 2; FPI, 3; HPI, 4) and [(h4-C8H 12)RhCl(L)] (L = CPI, 5; NOPI, 6; FPI, 7; HPI, 8) have been synthesized from the reactions of [{(h3;h3-C 10H16)Ru(m-Cl)Cl}2] and [{(h4-C 8H12)RhCl}2] with 1-(4-cyanophenyl)imidazole (CPI), 1-(4-nitrophenyl)imidazole (NOPI), 1-(4-formylphenyl)imidazole (FPI) and 1-(4-hydroxy-phenyl)imidazole (HPI). Resulting complexes have been fully characterized and structures of [(h3;h3-C 10H16)RuCl2(NOPI)] (2), [(h4-C 8H12)RhCl(CPI)] (5) and [(h4-C 8H12)RhCl(NOPI)] (6) determined crystallographically. Crystal structures of 2, 5 and 6 revealed the presence of extensive inter- and intra-molecular C-H⋯X (X = O and Cl) and C-H⋯p interactions. © 2010 Elsevier B.V. All rights reserved.
Synthesis and characterization of ruthenium(II) complexes based on diphenyl-2-pyridylphosphine and their applications in transfer hydrogenation of ketones
(Elsevier S.A., 2011) Prashant Kumar; Ashish Kumar Singh; Mahendra Yadav; Pei-Zhou Li; Sanjay Kumar Singh; Qiang Xu; Daya Shankar Pandey
Synthesis and characterization of the ruthenium complexes [RuH(CO)Cl(κ1-P-PPh2Py)2(PPh 3)] (1) and [Ru(CO)Cl2(κ1-P-PPh 2Py)(κ2-P-N-PPh2Py)] (2) containing diphenyl-2-pyridylphosphine (PPh2Py) are described. Spectral and structural data suggested linkage of the PPh2Py in κ1-P bonding mode in 1 and both the κ1-P and κ2-P-N bonding modes in 2. The complex 1 reacted with N,N-donor bases viz., ethylenediamine (en), N,N′-dimethyl-(ethylenediamine) (dimen), 1,3-diaminopropane (diap), 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and di-2-pyridylaminomethylbenzene (dpa) to afford cationic complexes of formulation [RuH(CO)(κ1-P-PPh 2Py)2(N-N)]+ (3-8) [N-N = en, 3; dimen, 4; diap, 5; bipy, 6; phen, 7; and dpa, 8], which have been isolated as their tetrafluoroborate salts. The complexes under investigation have been characterized by elemental analyses, spectroscopic and electrochemical studies. Molecular structures of 2, 3, 6, and 8 have been determined by single crystal X-ray diffraction analyses. Further, the complexes 1-8 act as effective precursor catalyst in transfer hydrogenation of acetophenone/ketones in basic 2-propanol. © 2010 Elsevier B.V. All rights reserved.
Synthesis and characterization of some heteroleptic copper(II) complexes based on meso-substituted dipyrrins
(Springer India, 2011) Rakesh Kumar Gupta; Mahendra Yadav; Rampal Pandey; Daya Shankar Pandey
The syntheses and characterizations of meso-substituted dipyrrins, 5-(4-imidazol-1-yl-phenyl)- dipyrromethene (4-impdpm), 5-(4-nitro-imidazol-1-yl- phenyl)-dipyrromethene, (4-nimpdpm), 5-(4-benzimidazol- 1-yl-phenyl)- dipyrromethene (4-bimp-dpm) and heteroleptic complexes [Cu3(4-impdpm) 2(hfacac)2] 1, [Cu(4- nimpdpm)(acac)] 2, [Cu(4-nimpdpm)(hfacac)] 3, [{Cu(4-bimpdpm)(acac)}n] 4 and [{Cu(4-bimpdpm)- (hfacac)}n] 5, imparting acetylacetonato (acac) and hexafluoroacetylacetonato (hfacac) groups as co-ligand have been described. The dipyrrins and complexes 1-5 have been characterized by elemental analyses and spectral (IR ESI-MS, NMR, electronic absorption and emission) studies. Crystal structures of 1, 3 and 4 have been authenticated by X-ray single crystal analyses. The reaction between 4-impdpm and Cu(hfacac)2 gave a trimetallic complex, under analogous conditions 4-nimpdpm and 4-bimpdpm reacted with Cu(acac)2 and Cu(hfacac)2.2H2O to afford mononuclear (2, 3) and 1D polymeric (4, 5) complexes. © Indian Academy of Sciences.
Synthesis and characterization of some novel ruthenium(II) complexes containing thiolate ligands
(2010) Prashant Kumar; Mahendra Yadav; Ashish Kumar Singh; Daya Shankar Pandey
Reactions of the ruthenium complexes [RuH(CO)Cl(PPh3)3] and [RuCl2(PPh3)3] with hetero-difunctional S,N-donor ligands 2-mercapto-5-methyl-1,3,5-thiadiazole (HL1), 2-mercapto-4-methyl-5-thiazoleacetic acid (HL2), and 2-mercaptobenzothiazole (HL3) have been investigated. Neutral complexes [RuCl(CO)(PPh3)2(HL1)] (1), [RuCl(CO)(PPh3)2(HL2)] (2), [RuCl(CO)(PPh3)2(HL3)] (3), [Ru(PPh3)2(HL1)2] (4), [RuCl(PPh3)3(HL2)] (5), and [RuCl(PPh3)3(HL3)] (6) imparting κ2-S,N-bonded ligands have been isolated from these reactions. Complexes 1 and 4 reacted with diphenyl-2-pyridylphosphine (PPh2Py) to give neutral κ1-P bonded complexes [RuCl(CO)(κ1-P-PPh2Py)2(HL1)] (7), and [Ru(κ1-P-PPh2Py)2(HL1)2] (8). Complexes 1-8 have been characterized by analytical, spectral (IR, NMR, and electronic absorption) and electrochemical studies. Molecular structures of 1, 2, 4, and 7 have been determined crystallographically. Crystal structure determination revealed coordination of the mercapto-thiadiazole ligands (HL1-HL3) to ruthenium as κ2-N,S-thiolates and presence of rare intermolecular S-S weak bonding interaction in complex 1. © 2010 Elsevier B.V. All rights reserved.
Synthesis, characterisation and theoretical studies on some piano-stool ruthenium and rhodium complexes containing substituted phenyl imidazole ligands
(2010) Ashish Kumar Singh; Prashant Kumar; Mahendra Yadav; Daya Shankar Pandey
Reactions of the chloro-bridged arene ruthenium complexes [{(η6-arene)RuCl(μ-Cl}2] (η6-arene = benzene, p-cymene) and structurally analogous rhodium complex [{(η5-C5Me5)RhCl(μ-Cl}2] with imidazole based ligands viz., 1-(4-nitro-phenyl)-imidazole (NOPI), 1-(4-formylphenyl)-imidazole (FPI) and 1-(4-hydroxyphenyl)-imidazole (HPI) have been investigated. The resulting complexes have been characterised by elemental analyses, IR, 1H and 13C NMR, electronic absorption and emission spectral studies. Crystal structure of the representative complex [(η5-C5Me5)RhCl2(NOPI)] has been determined crystallographically. Geometrical optimisation on the complexes have been performed using exchange correlation functional B3LYP. Optimised bond lengths and angles of the complexes have been found to be in good agreement with our earlier reports and single crystal X-ray data of the complex [(η5-C5Me5)RhCl2(NOPI)]. © 2009 Elsevier B.V. All rights reserved.
Synthetic, spectral, structural, and catalytic aspects of some piano-stool complexes containing 2-(2-Diphenylphosphanylethyl)pyridine
(Wiley-VCH Verlag, 2010) Prashant Kumar; Mahendra Yadav; Ashish Kumar Singh; Daya Shankar Pandey
Reactions of the complexes [(η5-C5H 5)Ru(PPh3)2Cl], [{(η6a:rene) Ru(μ-Cl)Cl}2] (η6-arene = C6H 6, C10H14, and C6Me6) and [(η5-C5Me5)M(-Cl)Cl)2] (M = Rh, Ir) with 2-(2-diphenylphosphanylethyl)pyridine (PPh2Etpy) were investigated. Neutral κ1-P-bonded complexes [(η5-C5H5)Ru(κ1-PPPh 2EtPy)(PPh3)Cl] (1) and [(η6-arene] Ru(κ1-P-PPh2EtPy)Cl2 [arene = C 6H6, (2). C10H14, (3), and C 6Me6, (4)] were isolated from the reactions of [(η5-C5H5)Ru(PPh3) 2Cl] and [{(η6-arene)Ru(-Cl)Cl}2] with PPh2EtPy. Treatment of 1-4 with NH4BF4/ NH 4PF6 in methanol allows the synthesis of cationic κ2-P,Nchelated complexes [(η5-C 5H5)Ru(K2-P,N-PPh2EtPy)(PPh 3)]+ (5) and [(η6-arene) Ru(κ2-P-N-PPh2EtPy)Cl]+ [arene = C 6H6, (6), C6H14, (7), and C 6Me6 (6)]. On the other hand, the dimers [{(η5-C5Me5)M(-Cl)Cl}2] (M = Rh or Ir) reacted with PPh2EtPy in methanol to afford cationic κ2-P,N-chelated complexes [(η5-C 5Me5)M(κ2-P-N-PPh2EtPy)Cl] + [M = Rh, (9); Ir, (10)]. Complex 10 reacted with an excess amount of sodium azide or sodium, chloride to afford the complexes [(η5- C5Me5)Ir(κ1-P-PPh2EtPy)X 2] (X = N3- 11; Cl-, 12), establishing the hemilabile nature of the coordinated PPh2EtPy. The complexes were characterized by elemental analyses and various physicochemical techniques. The molecular structures of 1, 5, 6, 9, and 10 were determined crystallographically, and the catalytic potentials of 1-10 were evaluated towards transferhydrogenation reactions under aqueous conditions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA,.