Pabitra K. Bhattacharya

Epoxidation of alkenes with iodosylbenzene using mono-and binuclear Ru(III)-Schiff base complex catalysts

Abstract Mono- and binuclear complexes of Ru(III) were synthesized using Schiff base ligands obtained by condensation of 2-pyridinecarboxaldehyde with 1,2- and 1,3- or 1,4-phenylenediamine, respectively. The complexes were characterized by analytical, spectral, conductance, cyclic voltammetry, and ESR studies. The epoxidation of alkenes was studied using these complexes as catalysts and iodosylbenzene as an oxidant. The complexes were found to be remarkably stable under the reaction conditions. Rates of the epoxidation of cis-cyclooctene using binuclear complexes were found to be nearly twice those using the mononuclear ones, indicating participation of both the metal centres of the former in the reaction. The absence of μ-oxo reaction product was shown by cyclic voltammetric studies. The mechanism of the reaction is suggested.

Mixed ligand complexes of chromium(III) and iron(III) : synthesis and evaluation as catalysts for oxidation of olefins

Abstract The mixed ligand complexes Cr III (dpa)(L)Cl and Fe III (dpa)(L)(H 2 O) n Cl (where dpa = dipicolinic acid, l = ethylenediamine, 2,2-bipyridine or 1,10-phenanthroline, n = 1 or 2) were synthesized and characterized by elemental analysis and spectral, magnetic, conductance and electrochemical studies. The complexes were evaluated for their activity as catalysts for the epoxidation of olefins. The chromium complexes catalyzed epoxidation of olefins, viz., norbornene, cis -cyclooctene, styrene and cyclohexene with iodosylbenzene, to give corresponding epoxides. Oxidation of cyclohexene gave allylic oxidation products besides the epoxide. The iron complexes were nearly inactive as epoxidation catalysts under these conditions. Spectrophotometric and electrochemical measurements were used to deduce the cause of low catalytic activity.

Epoxidation of olefins catalysed by Mn(III)-Schiff base complexes

Abstract Mn(III) complexes of Schiff base ligands have been synthesized by the reaction of MnCl 2 ·4H 2 O in ethanolic solutions with the Schiff bases obtained by the condensation of 1,3-diaminopropane or 1,3-diamino-2-hydroxypropane with salicylaldehyde, 2-hydroxynaphthaldehyde or 2-hydroxyacetophenone. The complexes were characterized by elemental analysis, IR spectral, thermogravimetric, conductance, magnetic susceptibility and FAB mass spectral studies. These complexes have been employed as catalysts for the epoxidation of olefins using iodosylbenzene as an oxidant. The efrect of OH substitution on the Schiff base ligand in the complex on its catalytic activity towards epoxidation has been studied.

Synthesis, characterisation and homogeneous catalytic activity study of Mn(II) and Fe(III) ternary complexes

Abstract The mixed ligand complexes of the type LFeACl· n H 2 O and LMnA·H 2 O where L is the mannich base obtained by hydrogenation of Schiff base ligands of salicylaldehyde and amino acids, and A is the bipyridyl or orthophenanthroline synthesised. These complexes were characterised by elemental analysis, spectral, magnetic, FAB mass spectral and electrochemical studies. These complexes have been used as catalysts for epoxidation of olefins like cyclohexene, cis-cyclooctene and norbornene using iodosylbenzene as the oxidant. In the epoxidation reactions using these complexes, it was found that Mn (II) complexes act as better catalysts compared to Fe (III) complexes. The mechanism of the progress of the oxidation reaction and termination of catalytic activity has been investigated by using spectral and electrochemical studies.

Synthesis and characterisation of some Ru(II) complexes of 2-carbamoylpyridine derivatives

Abstract p -Substituted N -phenyl derivatives of 2-carbamoylpyridine (L) have been prepared by the reaction of pyridine-2-carboxylic acid with p -substituted aniline. Five complexes of the type [Ru(L)(DMSO) 2 Cl 2 ] have been synthesized by the reaction of [Ru(DMSO) 4 Cl 2 ] with L. The amide ligands have been characterized by elemental analysis, infra red and 1 H NMR spectral studies. The complexes are diamagnetic and show intense absorptions due to metal to ligand charge transfer (MLCT) transitions in the UV–visible spectra. The IR spectra of the complexes show that the amide ligands coordinate to the ruthenium (II) ion as a bidentate ligand coordinating from pyridyl nitrogen and from the carbonyl oxygen of the amide group. The complexes undergo a reversible ruthenium (II)–ruthenium (III) oxidation near 0.55 V in acetonitrile solution. The ruthenium (II)–ruthenium (III) oxidation potentials of the complexes are found to be sensitive to the nature of the substituent on the ligand.

Oxidation of organic substrates catalysed by mixed ligand RuIII complexes. Investigation of active catalytic species and termination pathway

Abstract The mixed ligand complexes of the type, [Ru III (DPA)(L)Cl] (where DPA=2,6-dipicolinic acid L=ethylenediamine, 2,2′-bipyridine or 1,10-phenanthroline) have been synthesised and characterised by spectral, magnetic and cyclic voltammetric studies. The complexes have been used as catalysts for the oxidation of hydrocarbons using iodosylbenzene and tert -butyl hydroperoxide as the oxidants. The formation of intermediate has been investigated in case of the oxidation reaction involving various oxidants and [Ru III (DPA)(2,2′-bipy)Cl] as a catalyst. It is observed that the same active intermediate, [Ru V (DPA)(2,2′-bipy)(O)], is formed for all of the oxidants. This intermediate catalytically transfers oxygen to the olefin and causes its oxidation. Termination of the catalytic activity is due to the formation of the μ-oxo dimer of the complex, which has been isolated and characterised by elemental analysis, spectral and cyclic voltammetric studies.

Synthesis of binuclear amide complexes of Ru(III) and study of their catalytic activity in epoxidation of alkenes

Abstract Syntheses of the binuclear amide complexes of Ru(III) are described. The catalytic activity of the complexes, which are highly soluble in water, was examined by carrying out the epoxidations of norbornene, cis -cyclooctene and trans -4-octene to give the respective oxides in the presence of the oxidant iodosylbenzene. The reactions were monitored by UV-Vis and R spectroscopy and cyclic voltammetry, and the reaction mechanism elucidated.

Study of copper(II) and nickel(II) ternary complexes involving tertiary amines and phenyl or hydroxylphenyl substituted amino acids

Abstract Formation constants of ternary complexes MAL, where M = Cu(II) or Ni(II). A = 2.2′bipyridyl. 1, 10-phenanthroline, and L = 3.4-dihydroxyphenylalanine (dopa), tyrosine, or phenylalanine have been determined by using the computer program SCOGS. It is observed that dopa coordinates with Cu(II)-A and Ni(II)-A through the aminocarboxylate and only over the pH range 3–8, though the ligand coordinates with free Cu(II) ion from the amino carboxylate end in the lower pH range (pH 2–4) and from the catechol end at the higher pH range (pH > 5). The visible spectrum of Cu-A-dopa is similar to that of Cu-A-phenylalanine or Cu-A-tyrosine over the entire pH range, confirming amino carboxylate coordination. Δ log K ( K MAL - log K ML ) is found to be positive in all the six Cu(II) complexes. whereas it is negative in Ni(II) complexes. Release in the ternary complexes of the repulsion between the Cu(II) d π electron and electrons delocalized over the phenyl ring has been proposed as a probable reason for the positive Δ log K .

Synthesis and substitution reactions of dichlorobis-triphenylphosphine[2-(N-(2-pyridinium-2-yl)-carbamoyl-N−)-pyridine]ruthenium(II)

Abstract Spectroscopic and crystallographic studies show that 2-(N-(2-pyridyl)carbamoyl)pyridine (HL) in both its neutral and deprotonated forms, coordinates ruthenium(II) via the amidato- and pyridine-nitrogen atoms thereby forming five-membered rings. In neutral [Ru(HL)(PPh3)2Cl2], HL exists as a zwitterion and the molecular structure is stabilised, in part, by an intramolecular Cl⋯N interaction. Reaction of the title complex with bidentate chelating ligands leads to the replacement of two chlorides by the bidentate ligands, resulting in the formation of the mixed-ligand complexes. There is deprotonation of the zwitterionic HL in the mixed-ligand complexes.

Alkene epoxidation with iodosylbenzene catalysed by mono and binuclear Mn(II)-Schiff base complexes

Abstract Binuclear metal-Schiff base complexes [Mn 2 (PA 2 ppd) 2 Cl 4 ] ( I ), [Mn 2 (PA 2 mpd) 2 Cl 4 ] ( II ) and a mononuclear complex [Mn(PA 2 opd)Cl 2 ] ( III ) were synthesised and characterized. The complexes I–III were used as catalysts for the epoxidation of olefins with iodosylbenzene as an oxidant in acetonitrile-water solvent mixture. Binuclear complexes I and II selectively catalysed the epoxidation, whereas the mononuclear complex III was unselective. Among the binuclear, the complex having a m -phenyl-enediamine bridge was superior to the one with a p -phenylenediamine bridge as the catalyst for the epoxidation of olefins. The effect of addition of nitrogen bases on the catalytic activity of ( II ) was also studied.