M. Ravindranathan

Synthesis and catalytic activity of Fe(III) anchored to a polystyrene–Schiff base support

Cross-linked styrene-divinylbenzene copolymer was functionalized into bidentate Schiff base bearing ligands. Immobilization of iron(III) on to the polymer matrix resulted in the synthesis of catalytically active metal complexes. These supported catalysts were found to be effective in the epoxidation of cis-cyclooctene and styrene in presence of tert-butylhydroperoxide under mild conditions. The influence of various reaction parameters on conversion and selectivity to products of epoxidation has been discussed.

A study of synthesis, characterization and catalytic hydrogenation by polymer anchored Pd(II)-amino acid complexes

Abstract l -Valine was anchored to 6% and 8% cross-linked poly(styrene-divinyl benzene) resin and its complex with palladium chloride was prepared. The newly synthesized catalysts were characterized by various techniques such as elemental analysis, FT-IR, DRS, SEM and TGA. Physico-chemical properties like surface area, swelling behavior in different solvents, bulk density, etc. have been determined. The polymer supported Pd complexes behave as versatile and recyclable catalysts for the hydrogenation of 1-octene, cyclohexene, acetophenone and nitrobenzene. Kinetics of hydrogenation of 1-octene has been investigated in detail. The influence of different reaction parameters on conversion and selectivity to products are reported.

Codimerization of 2,5-norbornadiene with ethylene using soluble cobalt and nickel catalysts

Abstract Co(acac) x -Dppe-Et y Al 2 Cl 6- y ( x =2, 3; y =3,4) system promotes the codimerization of 2,5-norbornadiene ( 1 ) with ethylene to give a mixture of 3-vinylnortricyclene ( 2 ), 5-vinyl-2-norbornene ( 3 ) and deltacyclane ( 4 ). A maximum turnover (C 9 /Co) of 46.3 for the codimers is achieved with the cobalt system. On Ni(acac) 2 -Dppe-Et y Al 2 Cl 6- y , ( y =2,3) system 1 and ethylene selectively codimerize to give 3 and 5-ethylidene-2-norbornene ( 5 ) in the temperature range −5 to −30°C in CH 2 Cl 2 solvent. The influence of various solvents, ligands, Lewis acids and β-diketone ligands on yield and selectivity of the products are investigated. The maximum turnover of this catalyst system for the formation of codimer is 16.6. The probable mechanisms for formation of the products are delineated.

Catalytic epoxidation of olefins by polymer-anchored amino acid ruthenium complexes

Abstract A synthetic strategy was developed to anchor an amino acid l -valine on to styrene–divinylbenzene co-polymer beads with 8% and 6% cross linking. The polymeric ligands containing bidentate N,O donor sites were treated with a solution of ruthenium(III) chloride to form the metal complex on the support. These immobilized Ru(III) complexes were characterized by elemental analysis, FT-IR, UV–visible diffuse reflectance, ESR, SEM and thermal analysis. The catalytic epoxidation of styrene, norbornylene, cyclooctene, and cyclohexene were investigated using the supported catalysts in the presence of tert.-butyl hydroperoxide as the terminal oxidant. Selective epoxide formation was observed with norbornylene and cis-cyclooctene whereas in the case of styrene the corresponding epoxide, benzaldehyde and acetophenone were obtained. Amongst the olefins screened, good activity was observed in the case of cyclohexene. The effect of various reaction parameters as well as some aspects of catalyst recycling and possible mechanistic pathways has also been investigated.

Dimerization of ethene to 2-butene and metathesis with 1-butene by sequential use of homogeneous catalyst systems

Abstract Ethene has been dimerized selectively to 2-butene (cis+trans) employing a catalyst system consisting of Ni(acac)2 and Et3Al2Cl3. 2-Butene undergoes metathesis with 1-butene formed in the dimerization of ethene on a WCl6-Et3Al2Cl3 additive system. As a result of metathesis propene and 2-pentene are obtained in varying selectivities.

Dimerization of ethylene catalyzed by β-diketonate complexes of cobalt and nickel

Abstract The M(acac)n-Rx Al2Cl6−x (M = Co, n = 2 or 3; Ni, n = 2; R = Et, i-Bu) system, both in the presence and absence of additives, is used for the dimerization of ethylene to a mixture of olenns consisting predominantly of 2-butenes. With the Co(acac)3-Al(i-Bu)3 system, a maximum conversion of 76% with selectivity to 2-butenes of 98 is achieved at 25 °C and 8 kg cm−2 ethylene pressure. Selectivity to 2-butenes is higher with the Co(III) complex compared to Co(II) in combination with trialkylaluminum. However, the three-component Co(acac)2-Et2AlCl-PR3 system is superior to Co(acac)3-Et2AlCl-PR3 for the dimerization of ethylene to 2-butenes. The activity of Co(R1COCHCOR2)2 in combination with alkylaluminum cocatalysts decreases when R1, R2 in the complex are Ph, Ph > CH3, CH3 > Ph, CH3 > CF3, CF3 for AlEt3 and CF3, CF3 > Ph, Ph > Ph, CH3 > CH3, CH3 for Et3Al2Cl3. For Ni(acac)2-Et2AlCl-PR3, the selectivity to 2-butenes decreased in the following order for PR3: P(n-Bu)3 ≈ DIPHOS > PPh3 > P(OPh)3. The effects of ethylene pressure and reaction temperature on the activity and selectivity to 2-butenes are also investigated.

Disproportionation, isomerization and de-tert-butylation of 2,6-di-tert-butylphenol catalyzed by H-MCM-41

Mesoporous H-MCM-41 is an efficient catalyst for conversion of 2,6-di-tert-butylphenol to 2-tert-butylphenol, 2,4,6-tri-tert-butylphenol, 2,4-di-tert-butylphenol and 4-tert-butylphenol besides di- and tri-isobutylene in solvent free conditions. At low temperature (100 °C) and shorter reaction times 2-tert-butylphenol and 2,4,6-tri-tert-butylphenol are major products whereas at high temperature (180 °C) 4-tert-butylphenol is the most favoured product. H-MCM-41 steamed for 6 h at 520 °C was found to be the most active catalyst with maximum turnover of the products.

Oligomerization of dec-1-ene over montmorillonite clay catalysts

The Bronsted acid sites generated on Montmorillonite-K10 and other cation (Al3+, Zr4+, H+) exchanged clays when evacuated at high temperature are quite active for oligomerization of dec-1-ene in liquid phase.

Aspects of tautomerism. Part V. Solvent, substituent, and steric effects on the ring–chain tautomerism of o-benzoylbenzamides

Ring-chain tautomeric equilibria of o-benzoylbenzamides in 95% ethanol, chloroform, dioxan, and acetonitrile have been estimated using u.v. spectroscopy. Unlike the case of acids, solvent polarity has only a small effect. In ethanol the cyclic form is favoured. Electron-withdrawing groups in the amide-bearing ring disfavour the cyclic form. Substitution of methyl, ethyl, and phenyl groups on the nitrogen atom of the amide function results in increase of the proportion of the cyclic form in the first two cases and decrease in the last.

Catalytic hydrogenation by recyclable supported Pd(II)-amino acid complex

L-phenyl alanine was anchored to P(S-DVB) resin and its complex with PdCl2 was prepared. The newly synthesized catalyst was found to be a versatile and recyclable catalyst for the hydrogenation of 1-octene and acetophenone. This chiral catalyst induced moderate enantioselectivity during the asymmetric reduction of acetophenone.