K.N. Bhatt

Asymmetric epoxidation of styrene by novel chiral ruthenium(II) Schiff base complexes, synthesis and characterization.

Abstract Synthesis of some novel Chiral Ru(II) Schiff base complexes of the type [RuL(PPh3)(H2O)2] 1–6 where L = Chiral Schiff bases derived from salicylaldehyde and L-amino acids namely, L-alanine, L-valine, L-Serine, L-Arginine, L-Cystein and L-aspartic acid are reported. The characterisation of the complexes has been accomplished by microanalysis. IR-,UV/visible,[1H], 13C[1H] and 31P[1H] NMR spectroscopy, conductance measurements, electrochemical studies, optical rotation and circular dichroism soectroscopy. The conformational aspects regarding the asymmetric arrangement of substituents R at aminoacid moiety of the Schiff bases around Ru(II) metal ion has been discussed. The complexes show quasireversible behaviour and the redox potential of Ru(II)/Ru(I) couple lie in the range −0.34 to −0.18 volts. In the asymmetric epoxidation of styrene by the complexes 1 – 6 and idosylbenzene, we observed that on employment of the R form of the catalyst resulted in the formation of (S) styrene oxide as dominant enantiomer by GLC and NMR. Enantiomeric excess for the resulting epoxides were determined by [1H] NMR spectroscopy using Chiral shift reagent, tris[3-(heptafluoropropyl hydroxymethylene − (+) camphoratoleuropium(III), Eu(hfc)3.

First report on highly efficient alkene hydrogenation catalysed by Ni(salen) complex encapsulated in zeolite

Ni(salen) (salen = bis-(salicylidene)ethylenediamine) complex was encapsulated in zeolite Y and hydrogenations of cyclohexene, cyclooctene, 1-hexene and benzene were carried out with Ni(salen) encapsulated zeolite at moderately high temperature (40°C) and pressure (60 atm of H2).

Hydrogenation of benzene to cyclohexane catalyzed by rhodium(I) complex supported on montmorillonite clay

Abstract[Rh(I)PPh3]+ intercelated in the interlamellars of montmorillonite clay catalyzes the hydrogenation of benzene to cyclohexane at 70°C and 20 atm hydrogen pressure.Abstract[Rh(I)PPh3)]+, добавленный к прослойкам глины монтморил-лонита, катализирет гидрирование бензола до циклогек-сана при 70°C и давлении водорода −20 атм.

Hydroformylation of allyl alcohol catalysed by (Rh(PPh3)3)+/montmorillonite: A kinetic study

Abstract Rh(PPh 3 ) 3 Cl complex exchanged with modified montmorillonite clay at room temperature gave a (Rh(PPh 3 ) 3 ) + species, 1 , anchored in the hydration layers of the clay. Hydroformylation of allyl alcohol catalysed by 1 at 70°C and 60 atm of CO+H 2 (1:1) gave Γ-hydroxybutyraldehyde (96%) and 2-methyl-3-hydroxypropionaldehyde (4%). The kinetics of hydroformylation of allyl alcohol catalysed by 1 was studied in the concentrations range of catalyst 0.1 to 0.75 mM, allyl alcohol 0.025 to 0.25 M, CO+H 2 (1:1) pressure 5 to 30 atm and temperature between 70 to 90°C. The rates of hydroformylation of allyl alcohol catalysed by 1 showed a first order dependence with respect to catalyst, allyl alcohol (up to 0.1 M), CO and H 2 concentrations respectively. Substrate inhibition effect was observed when the substrate/catalyst mole ratio exceeds 440. The insoluble catalyst residue formed during substrate inhibition runs showed an IR stretching at 630 cm −3 which was attributed to the formation of Rh II -allylic complex. Repeated use of the separated catalyst for 60 h showed no loss in catalytic activity in hydroformylation of allyl alcohol.

Ruthenium(III)-Schiff base complex-catalyzed carbonylation of nitrobenzene to give phenylurethane

Abstract Ruthenium(III)—Schiff base complexes of the type [RuIIIL Xn=1 or 2] where L = Schiff base such as bis(naphthaldehyde)-o-phenylenediimine (naphoph), bis(naphthaldehyde)ethylenediimine(naphen), bis(naphthaldehyde) propylenediimine (naphprop) and bis(naphthaldehyde)-diethylenetriimine (naphdien); X = Cl; catalyze the carbonylation of nitrobenzene at 160 °C and 15 atm CO partial pressure in ethanol to give a clean product, phenylurethane. The turnover rates observed after a reaction time of 2 h are in the range 5–22 mol product per mol catalyst per hour. The activity of the Ru(III)—Schiff base complexes screened in the carbonylation of nitrobenzene decrease in the following order: K[Ru(naphoph)Cl2]>K[Ru(naphen)Cl2]>K[Ru(naphprop)Cl2> [Ru(naphdien)Cl].

Catalysis of alkene hydrogenation and oxidation by nickel-saloph complex ; a novel bifunctional catalyst

Abstract Hydrogenation of cyclohexene to cyclohexane and cyclooctene to cyclooctane with H2 in presence of Ni(saloph), 1, (saloph = bis(salicylaldehyde)-o-phenylenediamine) were carried out at moderately high pressure (60 atm) and temperature (50°C) in ethanol medium. At normal temperature and pressure, the same catalyst (complex 1) catalyses the epoxidation of cyclohexene and cyclooctene with KHSO5 in presence of CTAB (cetyl trimethyl ammonium bromide; a phase-transfer reagent) in CH2Cl2. Cyclohexene oxide and cyclooctene oxide were found to be the major products of the epoxidation reactions.

Electrocatalytic oxidation of organic substrates with oxygen using ruthenium—Schiff base complex

Abstract Electrochemical behaviour of the ruthenium(III)—Schiff base complex [Ru III (Naphdien)Cl] 1 (Naphdienbis(2-hydroxynaphthaldehyde)diethylenetriaminato) was studied in the presence of benzoic anhydride, dioxygen, tetrabutylammonium perchlorate (TBAP) and organic substrates. Cyclic voltammetric findings confirm an ‘ECE’ pathway for the studied reactions. Controlled potential electrolysis experiments with cyclohexene, cyclooctene and triphenylphosphine at − 0.24 V ( vs. SCE) yielded primarily cyclohexene oxide, cyclooctene oxide and triphenylphosphine oxide with turnover rates of 2.3, 2.6 and 5.4 moles of product per mole catalyst per hour, respectively.

Epoxidation of cyclohexene with iodosylbenzene catalysed by Ru(III)—dmg and Ru(III)–dpg complexes: Synthesis and characterisation of catalytically active Ru(V)—oxo intermediates

Abstract The complexes K[Ru III (H—dmg) 2 Cl 2 ], 1 (dmg= dimethylglyoxime), and K[Ru III (H–dpg) 2 Cl 2 ], 2 (dpg=diphenylglyoxime), and the oxo complexes [Ru v (H–dmg) 2 (O)Cl], 3 , and [Ru v (H—dpg) 2 (O)Cl], 4 , were synthesised and characterised by elemental analysis, UV—Vis and IR spectroscopy and electrochemical studies. The epoxidation of cyclohexene with iodosylbenzene catalysed by complexes 1 and 2 is reported.

Kinetic study of [Ru(SALOPH)Cl2] complex-catalyzed oxidative carbonylation of methylamine to give methylurethane

Abstract The oxidative carbonylation of methylamine catalyzed by dichlorobis(salicylaldehyde-o-phenylenediiminatoruthenate(III) at 150 °C and CO + O2 (1:0.5) pressure of 21 atm gave methylurethane (80%), dimethylurea (15%) and N-methylformamide (5%) as the reaction products, with a turnover rate of 40 mol products per mole catalyst per hour. The rates of oxidative carbonylation measured at 150 °C and in the pressure range 5–21 atm, exhibited a first-order dependence with respect to catalyst, substrate and dissolved CO concentrations, while it was half-order with respect to dissolved O2 concentration. An activation energy of 9.2 kcal mol−1 was estimated from the measurements of rates of oxidative carbonylation of methylamine in the temperature range 150–170 °C.

Kinetics and mechanism of oxidation of diethylamine and triethylamine by [RuV=O(EDTA)]− in aqueous medium

Abstract The kinetics of oxidation of diethylamine and triethylamine by [Ru V =O(EDTA)] − were studied spectrophotometrically as a function of [Ru V =O(EDTA)] − and [amine] at a fixed pH of 5.0 and ionic strength of 0.2 M NaClO 4 . The reaction rate was followed by observing the disappearance of the characteristic peak at 393 nm of the oxo complex Ru V =O(EDTA) − with time. Oxidative N -dealkylation of tertiary and secondary amines produces secondary and primary amines respectively as oxidation products, the N -alkyl group being oxidized to the corresponding aldehyde. The oxidation reactions were studied at three different temperatures and activation parameters (Δ H ‡ and Δ S ‡) calculated. A mechanism involving a hydride shift from the α-carbon of the substrate to the oxo oxygen is proposed for the oxidation of amines by Ru V =O(EDTA) − . The experimental results are discussed with reference to the oxidation of the corresponding amines with molecular oxygen catalysed by the [Ru III (EDTA)(H 2 O)] − complex.