Heterogeneous Palladium Catalyst Research Articles

Hydrogenation of nitroarenes bearing aldehyde containing side chains over palladium and platinum catalysts: a new route to medium and large heterocyclic compounds

A wide range of nitroarenes bearing aldehyde containing side chains, readily available by hydroformylation of the corresponding alkenes have been hydrogenated over heterogeneous palladium or platinum catalysts to give medium and large heterocycles either resulting from direct cyclisation or by the formation of dimers. The yields of monomers and dimers are discussed as a function of ring size and the pattern of heteroatom substitution in the substrates; in general the greater the number of heteroatoms in the chain, the greater the yield of cyclic compounds.

Hydrogenation of carbon–carbon multiple bonds: chemo-, regio- and stereo-selectivity

Results of the last decade with respect to the selective hydrogenation of hydrocarbons with multiple unsaturation (dienes and alkynes) over heterogeneous palladium catalysts are reviewed. Factors such as metal dispersion, carbon deposits, and the use of promoters and additives controlling catalytic activities and chemo-, regio- and stereo-selectivity are discussed. A detailed treatment of the status of the selective removal of hydrocarbon impurities with multiple unsaturation from industrial feedstocks is also given.

ANESTHESIN SYNTHESIZED BY HYDROGENATION OF p-NITROBENZOIC ACID ETHYL ESTER ON PALLADIUM CATALYSTS

A technological scheme used for the commercial synthesis of anesthesin (p-aminobenzoic acid ethyl ester) includes the stage of reduction of p-nitrobenzoic acid ethyl ester (I) by iron cuttings in the presence of acetic acid. The reduction of ester I leads to the formation of anesthesin acetate, which is treated with sodium carbonate to obtain the target compound. The product is purified by recrystallization from ethanol in the presence of activated charcoal and sodium hydrosulfite in order to reduce and decolorize the soluble impurities [1]. The impurities present in the anesthesin represent for the most part the products of incomplete reduction of the nitro group, including p-nitrobenzoic acid ethyl ether (II), p-hydroxyaminobenzoic acid ethyl ester (III), and diethyl esters of azoxybenzene- (IV), azobenzene- (V), and hydroazobenzene- (VI) 4,4-dicarboxylic acids. The formation of anesthesin and semiproducts II – VI from the initial nitro compound I can be described by the following scheme: The rate of formation and the amount of the products of incomplete reduction of nitro groups depend on the temperature, solvent type, and nature of the reducing agent. In order to increase the yield of anesthesin, we have studied the process of hydrogenation of p-nitrobenzoic acid ethyl ester and the products of its incomplete reduction. The hydrogenation of ester I to the target compound (p-aminobenzoic acid ethyl ester) was carried out in the presence of a heterogeneous palladium catalyst Pd/C and palladium-containing anion exchangers AN-1 and AV-17-8 (an advantage of using the latter system in hydrogenation reactions was pointed out in [2, 3]). The results of preliminary investigations showed that, under the conditions selected, the hydrogenation of compounds I – VI proceeds in the kinetic regime and is a first-order process with respect to catalyst and hydrogen. However, dependence of the reaction rate on the substrate concentration was variable: when the substrate concentration became comparable to the concentration of active centers on the catalyst surface, the reaction order changed from zeroth to first. The plots of the effective hydrogenation rate constant for the initial nitro compound I versus palladium content in the catalyst (Fig. 1) exhibits an extremal shape. The reaction rate constant increases in proportion to the palladium content in the range of metal concentrations below 4 wt.%. The further increase in the metal content is accompanied by a decrease in the reaction rate, probably, because of a decrease in the catalytic activity caused by the growth of microcrystals. Thus,

Selective transfer dehydrogenation of aromatic alcohols on supported palladium

Transfer dehydrogenation of various alcohols has been investigated over heterogeneous palladium catalysts using olefins as hydrogen acceptors. Pd/Al2O3 together with cyclohexene is the most active and selective system, affording a simple and convenient laboratory synthesis of aromatic ketones in refluxing cyclohexane. Hydrogenolysis-type side reactions can be suppressed by minute amounts of a tertiary amine (selective poisoning of Pd). Aliphatic and cycloaliphatic alcohols are barely reactive under these conditions, a difference which offers the possibility of the selective transformation of aromatic alcohols even in the presence of an aliphatic OH group.

Activity enhancement by the support in the hydrogenation of C=C bonds over polymer-supported palladium catalysts

Four synthetic ion-exchange resins (AH, BH, CH, DH) of different hydrophilic/hydrophobic properties were used as supports for heterogeneous palladium catalysts (A, B, C, D). The resins contained styrene (STY) and 2-(methacryloxy)ethylsulfonic acid (MESA) as the comonomers. Either divinylbenzene (DVB: CH, DH resins) or N,N'-methylenebisacrylamide (MBAA: AH, BH resins) were used as the cross-linker. AH contained also N,N-dimethylacrylamide (DMAA) as the third comonomer. The catalysts (Pd 0.25-0.45% w/w) were obtained by ion-exchanging the acidic forms of the resins with [Pd(OAc)2] and reducing palladium(II) with excess sodium borohydride. The use of NaBH4 also ensured the neutralization of the acidic sites of the supports. No effect of the hydrophilic/hydrophobic properties of the supports was observed in the hydrogenation of cyclohexene and 2-cyclohexen-1-one in methanol, at 25 degrees C and 0.5, 1, and 1.5 MPa, respectively. However, catalysts A and B, containing amido groups provided by either DMAA or MBAA, proved to be more active than C and D. The observed activity enhancement was directly proportional to the nitrogen/ palladium molar ratio in the catalysts. This finding suggests that amido groups promote palladium through a direct interaction with the metal surface.

Heck reaction using palladium complexed to dendrimers on silica

Polyamidoamine dendrimers, constructed on the surface of silica, were phosphonated using diphenylphosphinomethanol (prepared in situ) and complexed to form a palladium-dimethyl TMEDA complex. This catalyst was found to be effective in the Heck reaction of aryl bromides with both butyl acrylate and styrene, affording coupling products in moderate to good yields. The heterogeneous palladium catalyst can also be recycled and reused with only moderate reduction in activity.Key words: dendrimer, Heck, palladium, silica.

Telomerization of butadiene with water catalyzed by heterogeneous palladium catalysts

The telomerization of butadiene with water in the presence of heterogeneous palladium catalysts was investigated. Among various heterogeneous palladium catalysts, palladium anchored on montmorillonite showed good activity and selectivity to octadienol comparable to those of a homogeneous palladium acetate catalyst. The palladium catalyst anchored on montmorillonite could be recycled with no loss in activity and selectivity.

Combined homogeneous and heterogeneous catalysts.: Rhodium carbonyl thiolate complexes tethered on silica-supported metal heterogeneous catalysts: olefin hydroformylation and arene hydrogenation

The rhodium carbonyl thiolate complex, Rh 2[μ-S(CH 2) 3Si(OCH 3) 3] 2(CO) 4 (Rh–S) was tethered to phosphine-modified Pd–SiO 2 (P–(Pd–SiO 2)), which was prepared by tethering the phosphine ligand Ph 2P(CH 2) 3Si(OC 2H 5) 3 to Pd–SiO 2, to give the tethered complex catalyst Rh–S/P–(Pd–SiO 2). Also, the phosphine-substituted Rh 2[μ-S(CH 2) 3Si(OCH 3) 3] 2[Ph 2P(CH 2) 3Si(OC 2H 5) 3] 2(CO) 2 (Rh–S–P) was tethered to several silica-supported metal heterogeneous catalysts M–SiO 2 (M=Pd, Pt, Ru, Ir) to give Rh–S–P/M–SiO 2. These complex catalysts, consisting of a tethered complex on a supported-metal (TCSM), were used to catalyze the hydroformylation of olefins and the hydrogenation of toluene under atmospheric pressure. In the presence of phosphorus donor-ligands, all the TCSM catalysts are active for the hydroformylation of olefins under the mild conditions of 60°C and 1 atm of H 2 and CO (1:1). The most active catalysts, Rh–S/P–(Pd–SiO 2) and Rh–S–P/Pd–SiO 2, give maximum TOF values of 1.04 and 0.88 (mol aldehyde/mol Rh min), respectively, and TO values of 905 and 703 (mol aldehyde/mol Rh) during 22.5 h and 23.5 h in the hydroformylation of 1-octene. The Rh–S–P/Pd–SiO 2∼PPh 3 catalyst system maintains its activity through three cycles and 68 h to give a total turnover of 2118 mol aldehyde/mol Rh. These activities are higher than those of the homogeneous rhodium thiolate complex catalyst (Rh–S–P) and the rhodium thiolate complex catalysts tethered on just SiO 2(Rh–S/P–SiO 2 and Rh–S–P/SiO 2). The effects of the phosphorus ligand and PR 3/Rh mole ratio on the hydroformylation rates, conversions, and chemo- and regioselectivities for aldehyde were also investigated. The Rh–S/P–(Pd–SiO 2) and Rh–S–P/Pd–SiO 2 catalysts are also active for the hydrogenation of toluene under the mild conditions of 40°C and 1 atm of H 2; they are much more active than the homogeneous rhodium thiolate complex catalyst Rh–S–P, the simple silica-supported heterogeneous palladium catalyst (Pd–SiO 2) and the rhodium thiolate complex catalysts tethered on just SiO 2(Rh–S/P–SiO 2 and Rh–S–P/SiO 2). The synergistic advantages of the two components (tethered complex and supported metal) of the TCSM catalysts are greater for the hydrogenation of toluene than for the hydroformylation of 1-octene.

ChemInform Abstract: The Alkylation of Iodouridine by a Heterogeneous Palladium Catalyst.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hydrocarboxylation of 1-(4-isobutylphenyl) ethanol catalyzed by heterogeneous palladium catalysts

Heterogeneous palladium catalysts were employed for the synthesis of 2-(4-isobutylphenyl) propionic acid (ibuprofen) by carbonylating 1-(4-isobutylphenyl) ethanol (IBPE) with carbon monoxide and water. Among the supported palladium catalysts tested, palladium anchored on montmorillonite showed good activity for the carbonylation and good selectivity to ibuprofen. For the palladium/montmorillonite catalyst, the presence of triphenylphosphine and hydrogen chloride in the reaction solution was essential for its catalytic activity even if triphenylphosphine and chloride ion had already been coordinated to the palladium precursor. The effects of reaction variables on the heterogeneous carbonylation have been investigated for the regiospecific synthesis of ibuprofen, and it was revealed that the palladium/montmorillonite showed better selectivity to ibuprofen than the homogeneous counterpart. This heterogeneous catalyst recovered by filtration after a batch of the reaction showed activity similar to that of the fresh catalyst for a new batch of reaction. Furthermore, the filtrate without the solid catalyst did not show any carbonylation activity. These implied that dissolution of palladium component from the solid catalyst had not been serious.

The Alkylation of Iodouridine by a Heterogeneous Palladium Catalyst.

The Alkylation of Iodouridine by a Heterogeneous Palladium Catalyst.

A new route to medium and large heterocyclic compounds

Hydrogenation of nitrobenzenes bearing aldehyde-containing substituents over heterogeneous platinum or palladium catalysts gives medium and/or large heterocyclic amines as a result of simple or dimeric cyclisation in moderate to good yields; a range of heteroatoms can be incorporated into the macrocycles, enhancing their potential as ligands.

Effective heterogeneous palladium catalysis of the reactions of organoboron compounds with aryl halides

Reactions of [Ph4B]Na and ArB(OH)2 with aryl halides are effectively catalyzed by heterogeneous palladium catalysts (PdCl2C, Pd(0)/C, and palladium black) to give cross-coupling products in high yields.

Synthesis of condensation polymers catalyzed by palladium-graphite

Palladium-graphite (PdGr) was applied to polycondensations as a heterogeneous palladium catalyst. Catalytic activities of PdGr for the Heck reaction and a carbonyl insertion reaction were investigated using the model reactions. Polycinnamamide was synthesized through the Heck reaction of N, N′-(3,4′-oxydiphenylene)bis(acrylamide) and bis(4-iodophenyl) ether catalyzed by PdGr. The polymerization proceeded efficiently in the presence of tributylamine, but required a long reaction time compared with the case of homogeneous catalysts. The resulting polymer was almost white in color, which means that it was less contaminated by palladium metal. The removal and recycling of PdGr were much easier than the case of homogeneous catalysts. Aramid was also synthesized through the carbonyl insertion reaction of m-diiodobenzene and bis(4-aminophenyl) ether catalyzed by PdGr. The rate of carbon monoxide consumption for the polymerization catalyzed by PdGr was almost equal to that catalyzed by the homogeneous palladium catalyst. In both cases, the structures of the resulting polymers were identical to those prepared by homogeneous palladium catalysts.

Heterogeneous palladium catalysts for the Heck reaction

The vinylation of iodobenzene with methyl acrylate was studied using palladium-based heterogeneous catalysts. Methyl cinnamate was formed as vinylation product and benzene as side product. All catalysts were of the type SiO 2X-(NH) 2-Pd-L 2, where L = P(C 6H 5) 3 or C 6H 5CN and X = Sn, Al or Ti. The catalysts were stable and could be reused several times in normal atmosphere without suffering appreciable loss in catalytic activity. The activity of the catalysts was good even at low temperature, and selectivities were very high. Strong interaction indicating the existence of chemical bonding was found between the modified silica support and palladium complex. A model of the active surface compound is proposed and confirmed.

ChemInform Abstract: Aryl Couplings with Heterogeneous Palladium Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Aryl couplings with heterogeneous palladium catalysts

The coupling reaction of diverse phenylboronic acids with aryl halogenides and -triflates has been performed by the use of simple palladium hydrogenation catalysts. Evidence for a heterogeneous type of catalysis has been obtained.

Rational design of a heterogeneous palladium catalyst for the selective hydrogenation of alkynes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRational design of a heterogeneous palladium catalyst for the selective hydrogenation of alkynesJudith G. Ulan, Wilhelm F. Maier, and David A. SmithCite this: J. Org. Chem. 1987, 52, 14, 3132–3142Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://doi.org/10.1021/jo00390a032RIGHTS & PERMISSIONSArticle Views1044Altmetric-Citations75LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts Get e-Alerts

Homogeneous catalysis with a heterogeneous palladium catalyst. An effective method for the cyclotrimerization of alkynes

Homogeneous catalysis with a heterogeneous palladium catalyst. An effective method for the cyclotrimerization of alkynes

Synthesis and catalytic properties of palladium complexes on polymeric supports in the hydrogenation of p-nitrochlorobenzene

1. By the competing ligand method, starting with bis(benzonitrile)palladium dichloride, complexes of palladium(II) have been immobilized on polymeric supports, including functional covers of nitrile, vinylpyridyl, vinylimidazole, allylamine, vinylcarbazole, and vinylpyrrolidone groups. Both molecules of benzonitrile in the original complex are replaced by the functional groups of the polymeric support, thus leading to structural homogeneity of the products that are formed. 2. Experiments on the hydrogenation of p-nitrochlorobenzene in the presence of homogeneous, heterogeneous, and heterogenized palladium catalysts have shown that the immobilization of palladium on polymeric supports improves the activity, selectivity, and stability of the catalysts.