Ferenc Notheisz

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).

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.

Novel clay intercalated metal catalysts: A study of the hydrogenation of styrene and 1-octene on clay intercalated Pd catalysts

Pd-hexadecylammonium montmorillonite (Pd-HDAM) catalysts have been prepared by a novel synthetic route. Sample characterization including XRD and TEM measurements confirmed the existence of interlayer Pd nanocrystallites which occupy clay particle defect sites. The catalytic activities of Pd-HDAM samples were tested by hydrogenation of 1-octene and styrene in the liquid phase. The reaction of styrene was found to be less dependent on the dispersion of Pd than that of 1-octene. The highest activities were observed for samples of low and medium Pd content. The application of various solvents made it possible to establish a correlation between the activities and the basal spacings dL of Pd-HDAM samples. When the value of dL exceeded 3 nm, interlamellar active sites became more accessible for reactants.

Low- and high-temperature hydrogenative ring-opening of alkyl-substituted cyclopropanes and methyloxirane over Pd/SiO2 catalyst: detection of β-hydride by a chemical method

The hydrogenative ring-opening of five alkyl-substituted cyclopropanes and of methyl-oxirane on Pd/SiO2 was studied at different temperatures in a closed circulation reactor. For cyclopropanes, the ring opens through simple hydrogenation, giving exclusively saturated hydrocarbons, whereas alcohols (hydrogenation), oxo compounds (isomerization) and also cracking products are produced from methyloxirane. The substituents exert significant effects on the regioselectivity of the reactions for both type of molecules. For the cyclic hydrocarbons, mechanistic pathways are discussed on the basis of the stereochemistry of the compounds and the characteristic features of the ring-opening rate vs. H2-pressure functions. Finally, a chemical method is proposed for the detection of β-hydride.

Transformation of carbon compounds on graphimet catalysts III. Structure and catalytic investigation of Pt graphimet

Abstract The hydrogenation of cyclohexene was studied over Pt-graphimet catalysts pretreated at 298 K. The platinum atoms are situated partly on the external surface of the graphite and partly in the interlayer space. The interlayer atoms are readily accessible for hydrogen, the mass transfer resistance is greater for oxygen, and the cyclohexene cannot diffuse into the interlayer space at all. Thus, the hydrogenation of cyclohexene takes place only on the exposed atoms on the external surface of Pt graphimet, and the atoms in the interlayer space are inactive in this reaction.

Heterogeneous asymmetric reactions, 33. Novel interpretation of the enantioselective hydrogenation of α-ketoesters on Pt/alumina-cinchona alkaloid catalyst system

The enantioselective hydrogenation of ethyl pyruvate (EtPy) was studied in toluene and in acetic acid, under identical reaction conditions (H2pressure 1 bar, Pt-alumina catalyst E 4759, dihydrocinchonidine (DHCD) concentration 0.001- 0.1 mmol/L). The DHCD concentration necessary for achieving maximal enantioselectivity (i.e. 80% ee in toluene and 90% ee in acetic acid) is higher by one order of magnitude in toluene than in acetic acid. This relatively high difference suggests a difference in reaction mechanism. This study calls attention to the formation of new chiral surface sites via chemisorption of DHCD on platinum atoms and the possible role of such sites in enantioselection.

Hydrogenative ring-opening reactions of alkyl-substituted cyclopropanes over Pt/SiO2 catalyst

Abstract The hydrogenative ring-opening reactions of five alkyl-substituted cyclopropanes [ethyl-(ECP), cis -1,2-dimethyl- ( c DMCP) and trans -1,2-dimethyl- ( t DMCP), 1,1-dimethyl-(1,1DMCP) and 1,1,2,2,-tetramethyl- (TMCP) cyclopropane] over Pt/SiO 2 catalyst were studied. The shapes of the curves depicting product formation rate vs. H 2 pressure suggest that CC as well as CH bond rupture occurs upon adsorption. Based on stereochemical considerations and on comparisons of product formation at the maximum rates, it is proposed that c DMCP forms a flat-lying complex over the surface of the catalyst and t DMCP, 1,1DMCP and TMCP react through edge-on surface intermediates. IR measurements concerning the reaction of ECP support the proposed dissociative adsorption.

Transformation of carbon compounds on graphimet catalysts IX. Structural properties and catalytic activity of Pd-graphimet

Abstract A comparative study of pristine and thermally treated (medium-temperature reduction, MTR, 573 K, 1h) Pd-graphimet was carried out to establish the changes arising in structure and catalytic activity. The structural investigation was performed by means of BET surface area analysis, transmission electron microscopy, small-angle X-ray scattering and H 2 titration. In order to distinguish between the hydrogenation and isomerization sites of the samples, the single turnover reaction of 1-butene was applied. For pristine Pd-graphimet, the experimental evidence confirmed the presence of interlayer metal and surface metal particles of different sizes. Although the catalytic activity was clearly attributable to the 1–2 nm surface Pd crystallites, the interlayer metal content also had an influence on the reaction through deintercalation which first started at 323 K. Nevertheless, the effect of MTR was found to be far more pronounced: all the inserted Pd atoms underwent migration and a moderate sintering of the surface Pd crystallites took place. Data on the transformation of 1-butene indicated that Pd-graphimet was similar in effect to supported Pd catalysts.