Ágnes Zsigmond

Zeolite-encapsulated cobalt salophen complexes as efficient oxygen-activating catalysts in palladium-catalyzed aerobic 1,4-oxidation of 1,3-dienes

Different cobalt salophen catalysts 1, 2, 3, and 4 were prepared and studied as oxygen-activating agents in the palladium-quinone catalyzed aerobic oxidation of 1,3-dienes. These cobalt salophen ca ...

Effect of substituents on the Mn(III)Salen catalyzed oxidation of styrene

Abstract Manganese(III)complexes of Salen, Br 2 Salen and ( tert -butyl) 4 Salen ligands and their encapsulated analogues were prepared by the intrazeolite ligand synthesis (template synthesis) method. The oxidation of styrene was studied on the above catalysts using molecular oxygen as oxidant and tert -butyl hydroperoxide as initiator. The progress of the reactions was followed both by gas chromatography and by the oxygen consumed. The effect of the substituents on the encapsulation, on the catalytic activity and the effect of the encapsulation on the catalytic activity were studied and discussed.

Comparative study of "ship-in-a-bottle" and anchored heterogenized Rh complexes

Abstract Heterogenized rhodium complexes were prepared by two different methods (“ship-in-a-bottle” and anchoring methods) and the catalysts were used in the hydrogenation of simple and prochiral alkenes. The “ship-in-a-bottle” type heterogenized rhodium complexes were active in the hydrogenation of hex-1-ene, cyclohexene, and 1-methylcyclohexene. At the same time the heterogenized catalyst had all the expected advantages of the heterogeneous system, namely easy handling and recyclability. The anchored catalyst could also catalyze the same hydrogenation reactions and showed all the advantages of the heterogeneous catalysts. However, the latter one was much more active in the above hydrogenation reactions than the “ship-in-a-bottle” type catalysts. Moreover, the anchored catalyst showed higher ee in the enantioselective hydrogenation of trans-2-methylpent-2-enoic acid than its encapsulated counterpart.

Ruthenium-Catalyzed Aerobic Oxidation of Alcohols on Zeolite-Encapsulated Cobalt Salophen Catalyst

A zeolite-encapsulated cobalt salophen catalyst was prepared by the intrazeolite ligand synthesis method. This catalyst proved to be active in the ruthenium-catalyzed oxidation of primary and secondary alcohols to aldehydes or ketones. Several advantages of the heterogenized catalyst was found in this system compared to the homogeneous counterpart, namely easy handling and better performance (less sensitive to solvent effects, higher specific rates).

The mechanism of hydrogenolysis and isomerization of oxacycloalkanes on metals: III. Effect of partial pressure of hydrogen on the selectivity of hydrogenolysis of oxacycloalkanes on Pt☆

The rates of hydrogenolysis and isomerization of methyloxirane, cis- and trans-2,3-dimethyloxirane and 2-methyloxetane were studied on a PtC catalyst, as functions of the hydrogen pressure and the temperature. A new phenomenon was observed in the case of 2-methyloxetane: the change in mechanism as the temperature was elevated led to a change in regioselectivity. There is no such effect for methyloxirane, for which the dissociative mechanism is not competitive at high hydrogen pressure. Likewise, the mechanisms of transformation of methyloxirane and the 2,3-dimethyloxiranes are not the same. Methyloxirane probably participated in edgewise adsorption on the surface of the catalyst, while cis-2,3-dimethyloxirane undergoes flat adsorption.

Stereochemistry of heterogeneous catalytic hydrogenolysis and isomerization of oxiranes

Abstract The hydrogenolysis and isomerization of methyloxirane and cis- and trans-2,3-dimethyloxirane were studied on Pt, Pd, and Ni catalysts in static and pulse microreactors. On Pt and Pd catalysts, considerable differences could be demonstrated between the rates of transformation of the cis and trans isomers, whereas on Ni catalyst there was scarcely any difference. It may be assumed that in the transformation of the trans isomer on Pt and Pd catalysts the rate-determining step is the formation of the 1,3-diadsorbed surface species; on the Ni catalyst, however, as in the case of 2-methyloxirane and the cis isomer on any of the three catalysts, the rate-determining step is the further reaction of the adsorbed surface species. The results obtained by the pulse reaction technique are indicative of the irreversible adsorption of the reactants. Besides contributing to the clarification of the mechanisms and stereochemistry of the reactions examined, the data obtained give a possibility for the explanation of the fundamental differences in regioselectivity on the Pt, Pd, and Ni catalysts. On Pt and Pd catalysts, the mechanism of formation of 1,3-diadsorbed surface species differs from the mechanism obtained on Ni catalyst.

Rate enhancement of oxidation reactions by the encapsulation of metal phthalocyanine complexes

Iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc) as free complexes as well as encapsulated in zeolite-Y (FePc-ZeY and CoPc-ZeY) have been studied as catalysts in mild, aerobic oxidation of hydroquinone. A remarkable rate enhancement was observed with the encapsulated catalysts, especially in the case of the encapsulated cobalt phthalocyanine, where the encapsulated complex was a good, active oxidation catalyst, while its homogeneous analogue was completely inactive. The site isolation effect is responsible for the observed rate enhancement. The solvent effect was also studied in the case of free complexes and encapsulated catalysts.

Enantioselective epoxidations catalyzed by zeolite MCM-22 encapsulated Jacobsen's catalyst

A novel method for the encapsulation of homogeneous catalysts within the supercages (7.1×18.2 Å) of zeolite MCM-22 has been developed. By way of example, the well known asymmetric oxidation catalyst (R,R)-N,N-bis(3,5-di-tert-butylsalicylidedene)-1,2-cyclohexanediaminemanganese(III) chloride, a.k.a Jacobsens catalyst, was occluded in MCM-22 during the zeolite synthesis. This ship-in-a-bottle complex exhibited both higher activity and enantioselectivity for the epoxidation of α-methylstyrene compared with the homogeneous catalyst.

The mechanism of hydrogenolysis and isomerization of oxacycloalkanes on metals. IV: Mechanism of transformation of oxiranes on Cu catalyst

The mechanism of isomerization of methyloxirane to propanal and acetone was studied on a Cu catalyst. During the transformation, the deoxidation reaction causes the oxidation of the catalyst surface, and Lewis acid site-basic site pairs are produced. Propanal is formed predominantly on these centers. The rate of formation of such active centers, and hence that of propanal, is maximum on the partially oxidized surface. Acetone is formed on the reduced metal surface. Both reactions may be regarded as hydroisomerization.

Selective oxidation of alkenes on a zeolite supported iron phthalocyanine catalyst

Abstract Iron phthalocyanine encapsulated in zeolites was used as oxygen activating cat.lysts in the triple catalytic aerobic oxidation of hydroquinone to benzoquinone, in the allylic oxidation of olefins and in the selective oxidation of terminal olefins to ketones. The catalyst proved active in the above reactions. It is stable towards self-oxidation and can be recovered and reused.