Palladium Carbon Research Articles

Oxazoline‐Mediated Interannular Cyclopalladation of Ferrocene: Chiral Palladium(II) Catalysts for the Enantioselective Aza‐Claisen Rearrangement

Formation of a carbon–palladium bond to the unsubstituted cyclopentadiene ring occurs during the cyclopalladation of 4-ferrocenyl-1,3-oxazolines and leads to a new type of metalated ferrocene (see scheme). These chiral complexes catalyze the asymmetric aza-Claisen rearrangement of allylic imidates.

Bimodal porous Pd–silica for liquid-phase hydrogenation

Palladium catalysts loaded on bimodal porous silica were examined in the liquid-phase hydrogenation of 2-butenal at 0 °C and a hydrogen pressure of 1.1 MPa. The sizes of mesopores and macropores of the silica support are controllable in the range of 4–23 nm and 0.5–25 μm, respectively. The macropores provide effective paths of mass transfer, and the mesopores present effective surfaces for dispersion of metals. The catalytic activity of Pd–silica with bimodal porous structure depends on the size of mesopores and macropores as well as on the particle size of the support silica. The most active Pd–silica catalyst, with mesopores of 12 nm and macropores of 2 μm, shows much higher activity than does a commercial palladium carbon catalyst without macropores. The results indicate that the diffusion process inside the catalyst particles dominantly determines the reaction rate in the hydrogenation.

Palladium‐Catalyzed Carbonylative Annulation of Terminal Alkynes: Synthesis of Coumarins and 2‐Quinolones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A novel highly regio- and diastereoselective haloamination of alkenes catalyzed by divalent palladium

From the readily available allylic alcohols or allylic amines, a novel Pd(II)–CuCl 2-catalyzed haloamination reaction of alkenes with high chemo-, regio-, and diastereo-selectivity was developed. The reaction proceeds through trans-aminopalladation of alkenes, followed by oxidative cleavage of the carbon–palladium bond with retention of configuration.

Comparisons of platinum, gold, palladium and glassy carbon as electrode materials in the design of biosensors for glutamate

Four electrode materials: Pt, Au, Pd and glassy carbon (GC), were studied to investigate their suitability as substrates in the development of two different classes of glutamate biosensor. Glutamate oxidase cross-linked onto poly( o-phenylenediamine) was chosen as the type 1 biosensor (PPD/GluOx), incorporating PPD as the permselective element to detect H 2O 2 directly on the electrode surface at relatively high applied potentials. GluOx and horseradish peroxidase/redox polymer modified electrodes (Os 2+PVP/HRP/GluOx) that relied on enzyme-catalysed H 2O 2 detection at lower applied potentials were used as type 2 biosensors. The voltammetric and amperometric responses to the enzyme signal transduction molecule, H 2O 2, and the archetypal interference species in biological applications, ascorbic acid, were determined on the bare and PPD/GluOx-modified surfaces. The amperometric responses of these electrodes were stable over several days of continuous recording in phosphate buffered saline (pH 7.4). The sensitivity of the type 1 biosensors to H 2O 2 and glutamate showed parallel trends with low limits of detection and good linearity at low concentrations: Pt>Au∼Pd⪢GC. Type 2 biosensors out-performed the type 1 design for all electrode substrates, except Pt. However, the presence of the permselective PPD membrane in the type 1 biosensors, not feasible in the type 2 design, suggests that Pt/PPD/GluOx might have the best all-round characteristics for glutamate detection in biological media containing interference species such as ascorbic acid. Other points affecting a final choice of substrate should include factors such as mass production issues.

Palladium-catalyzed carbonylative annulation of terminal alkynes: synthesis of coumarins and 2-quinolones

o-Iodophenols and o-iodoaniline derivatives react with terminal alkynes under 1 atm of CO in the presence of pyridine and catalytic amounts of Pd(OAc) 2 to generate coumarins and 2-quinolones, respectively, as the only products. Terminal alkynes bearing alkyl, aryl, silyl, hydroxyl, ester and cyano substituents are effective in these processes affording the desired products in moderate yields. The formation of coumarins and 2-quinolones in this process is in stark contrast with all previously described palladium-catalyzed reactions of o-iodophenols or o-iodoanilines with terminal alkynes and CO, which have afforded chromones and 4-quinolones. Moreover, under our reaction conditions terminal alkynes insert into the carbonpalladium bond instead of undergoing a Sonogashira-type coupling as confirmed by an isotope labeling experiment.

Rapid Removal of Benzyloxycarbonyl Groups from 1,4,7,10‐Tetraazacyclododecane Derivatives by Catalytic Transfer Hydrogenation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Selective and Efficient Catalyst for Carbonylation of Aryl Iodides: Dimeric Palladium Complex Containing Carbon—Palladium Covalent Bond.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Rapid Removal of Benzyloxycarbonyl Groups from 1,4,7,10-Tetraazacyclododecane Derivatives by Catalytic Transfer Hydrogenation

We report that N-benzyloxycarbonyl groups can be conveniently removed from 1,4,7,10-tetraazacyclododecanes by catalytic transfer hydrogenation with cyclohexene and 5% palladium–carbon catalyst. The process is rapid, selective, inexpensive, and is high yielding.

PdII-catalyzed cyclization of alkynes containing aldehyde, ketone, or nitrile groups initiated by the acetoxypalladation of alkynes.

The insertion of carbonyl or nitrile units into a carbon–palladium bond has been achieved under mild reaction conditions (see scheme). The PdII-catalyzed system, which does not require organometallic reagents, redox systems, or additives to obtain a high yield of cyclized product, is effective with a wide variety of functionalized alkyne compounds.

A synthesis of the phenolic lipid, 3-[( Z)-pentadec-8-enyl] catechol, (15:1)-urushiol

A synthesis of (15:1)-urushiol, urushiol monoene, 3-[( Z)-pentadec-8-enyl] catechol, 1,2-dihydroxy-3-[( Z)-pentadec-8-enyl] benzene, one of the toxic principles of Rhus toxicodendron and of Rhus vernicifera is described. 6-Chlorohexan-1-ol protected at the OH group with ethyl vinyl ether reacted with 2,3-dimethoxybenzaldehyde in the presence of lithium to give, after removal of the protective group with methanolic 4-toluenesulphonic acid, 1-(2,3-dimethoxyphenyl) heptane-1,7-diol. Catalytic hydrogenolysis in ethanol with palladium–carbon selectively afforded 7-(2,3-dimethoxyphenyl)heptane-1-ol accompanied by a small proportion of the 7-(3-methoxyphenyl)heptane-1-diol, formed by demethoxylation. Reaction of the dimethoxy compound with boron tribromide resulted in both bromination and demethylation to give 7-(2,3-dihydroxyphenyl) heptylbromide. This bromide in tetrahydrofuran (THF) containing hexamethylphosphoric triamide reacted with excess lithium oct-1-yne to give 3-(pentadec-8-enyl)catechol which, by catalytic hydrogenation in ethyl acetate containing quinoline, selectively formed the required cis product, 3-[( Z)-pentadec-8-enyl]catechol which was identical chromatographically and spectroscopically with urushiol monoene separated from the natural product.

Intramolecular CN bond formation in the reductive elimination of ortho-palladated arylhydrazones of acetophenone

Carbonylation in dichloromethane at room temperature of the dimeric ortho-palladated complex [Pd{C 6H 4C(CH 3)NNHC 6H 5}(μ-Cl)] 2 yields in a first step the monocarbonyl [Pd{C 6H 4C(CH 3)NNHC 6H 5}Cl(CO)] which very slowly (days) undergoes in solution reductive elimination of palladium to give high yield of the isoindolinone derivative, 2-anilino-3-methylene-isoindolin-1-one. Addition of the stoichiometric amount of NaOMe to the monocarbonyl complex [Pd{C 6H 4C(CH 3)NNHC 6H 5}Cl(CO)] in solution leads instantaneously to reductive elimination and affords the indazole derivative, 3-methyl-1-phenyl-indazole, in high yield. Carbonylation of the related complex [Pd{C 6H 4C(CH 3)NNHC 6H 4 -p-NO 2}(μ-Cl)] 2 yields in solution the monocarbonyl [Pd{C 6H 4C(CH 3)NNHC 6H 4 -p-NO 2}Cl(CO)] which in minutes affords high yield of the isoindolinone derivative, 2-(4-nitroanilino)-3-methylene-isoindolin-1-one. Such different behaviour sheds light on the mechanistic grounds that govern the intramolecular CN bond formation and the cyclization of ortho-palladated acetophenonearylhydrazones, and shows that the acidity of the NH bond controls the rate of the reactions. The requirement of the formation of a palladium–nitrogen amido bond cis to a palladium–carbon bond is supported for these results. We suggest that a tautomeric equilibrium of the hydrazonato ligand accounts for the two alternate pathways.

Analytical Performance of a Glucose Biosensor Prepared by Immobilization of Glucose Oxidase and Different Metals into a Carbon Paste Electrode

Enzymatic metallized carbon paste electrodes prepared by incorporation of mixtures of different metals into the paste offer a substantial decrease in the overvoltage for hydrogen peroxide oxidation and reduction. Dramatic improvements in the sensitivity and selectivity for glucose determination were obtained after the addition of iridium into carbon paste electrodes (CPE) containing glucose oxidase and palladium, copper or ruthenium. In all cases a synergistic effect was observed with a large enhancement in sensitivity obtained specially in the case of palladium-composite materials. The improvement in selectivity was more evident in the case of copper and palladium carbon paste enzymatic electrodes containing iridium where even in the presence of large excess of ascorbic acid, uric acid and acetaminophen, no interference was observed. A linear relationship between current and glucose concentration was obtained up to 1.5×10−2 M (2.7 g/L) glucose in the case of Pd(2.65%)-Ir(8.00%)-GOx(7.00%)-CPE. The effect of metals and enzyme content on the analytical performance of the bioelectrodes is analyzed.

The marked influence of steric and electronic properties of ancillary pyridylthioether ligands on the rate of allene insertion into the palladium–carbon bond

Neutral methyl- and acyl-palladium chloro complexes containing pyridylthioether ancillary ligands (R′NSR) (R′=H, Me, Cl; R=Me, Et, i-Pr, t-Bu, Ph) have been synthesised and characterised by elemental analysis and spectroscopic methods. The reactivity of these complexes toward allene (allene=DMA=1,1-dimethylpropadiene; TMA=1,1,3,3-tetramethylpropadiene) insertion into the palladium–carbon bond has been studied by 1H-NMR and UV–vis techniques. The rate of reaction appears to be strongly influenced by the steric and electronic properties of the ancillary ligand. The distortion induced by the substituent R′ in position 6 of the pyridine ring on the main coordination plane of the substrate (allowed by sulphur sp 3 hybridisation) renders the substrate itself more prone to nucleophilic attack by the allene. The rate of allene insertion can further be enhanced by lowering the basicity of the chelating atoms in the NS moiety which results in an increase of electrophilicity of the palladium core, so that the rate constants measured in the case of the complexes containing the ligand 6-chloro-2-phenylthiomethylpyridine (ClNSPh) are by far the greatest observed so far for similar reactions. Furthermore, on the basis of the indications emerging from the exhaustive study on the behaviour of all the related pyridylthioether methyl complexes, an associative asynchronous bond making mechanism for the rate determining nucleophilic attack by allene is proposed.

ChemInform Abstract: Role of Halide Ions in Divalent Palladium‐Mediated Reactions: Competition Between β‐Heteroatom Elimination and β‐Hydride Elimination of a Carbon—Palladium Bond.

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.

Carbon nanofiber supported palladium catalyst for liquid-phase reactions: An active and selective catalyst for hydrogenation of cinnamaldehyde into hydrocinnamaldehyde

Carbon nanofibers (CNFs) prepared by decomposition of ethane over a Ni/alumina catalyst, are used as support for palladium clusters. The carbon support displays a mean diameter of 40–50nm, lengths up to several tens of micrometers, as highlighted by transmission electron microscopy (TEM) observations and a specific surface area of about 50m2/g. The spheroidal palladium particles have a relatively homogeneous and sharp size distribution, centered at around 4nm. This novel Pd/carbon nanofiber catalyst displays unusual catalytic properties and is successfully used in the selective hydrogenation of the CC bond in cinnamaldehyde at a reaction temperature of around 80°C, under continuous hydrogen flowing at atmospheric pressure. The high performances of this novel catalyst in terms of efficiency and selectivity are, respectively, related to the inhibition of the mass-transfer processes over this non-porous material and to peculiar palladium–carbon interactions. It is concluded that the absence of microporosity in the carbon nanofibers favours both the high activity and selectivity which is confirmed by comparison with the commercially available high surface area charcoal supported palladium catalyst.

Coordination of Lewis acid to eta(2)-enonepalladium(0) leading to continuous structure variation from eta(2)-olefin type to eta(3)-allyl type.

The reaction of alpha,beta-unsaturated carbonyl compounds, a palladium(0) complex, and Lewis acids led to the formation of a new class of complexes showing a wide variety of structures with eta(2)-type and eta(3)-type coordination of the carbonyl compounds. The reaction of Pd(PhCH=CHCOCH(3))(PPh(3))(2) with BF(3).OEt(2) or B(C(6)F(5))(3) quantitatively gave palladium complexes 1a,b having BX(3)-coordinated eta(2)-enonepalladium structure, as revealed by X-ray structure analysis of the B(C(6)F(5))(3) adduct 1b. On the other hand, the reaction of Pd(PhCH=CHCHO)(PPh(3))(2) with BF(3).OEt(2) or B(C(6)F(5))(3) gave distorted zwitterionic eta(3)-allylpalladium complexes 3a,b, where the Pd-carbonyl carbon distance in 3a (2.413(4) A) is much shorter than that (2.96(1) A) in 1b. The values of the P-P coupling constant and (13)C chemical shift for carbonyl carbon are useful criteria for predicting how the eta(3)-coordination mode contributes to the structure of the enone-palladium-Lewis acid system. Molecular orbital calculations on the series of model complexes suggest that orbital overlap in the highest occupied molecular orbital between the palladium and carbonyl carbon is enlarged by coordination of the Lewis acid to the carbonyl group. Palladium-catalyzed conjugate addition of R-M (R-M = AlMe(3), AlEt(3), ZnEt(2)) and its plausible reaction path are also reported.

Theoretical study of carbon dioxide coordination in palladium complexes

Activation of the relatively inert CO 2 molecule to form higher organic molecules has been a focus of research for many years. Therefore, the coordination of CO 2 to transition metal fragments is of considerable interest. The coordination of CO 2 to transition metals may involve η 1 -O, η 1 -C, or η 2 -C,O bonding. The η 1 -C, or η 2 -C,O coordination with both early and late transition metal complexes are known. The ancillary ligands on the metal can play a significant role in effecting coordination of CO 2 to the metal center. Here we report a theoretical study of coordination modes of carbon dioxide to palladium complexes. The theoretical geometry and energies of a series of phosphine-substituted palladium carbon dioxide complexes, (PR 3 ) 2 Pd(CO 2 ), were investigated. The phosphine ligands included PH 3 , PMe 3 , PCy 3 , PMe 2 Ph, PMePh 2 , PPh 3 , P(OCH 3 ) 3 , P (CH=CH 2 ) 3 , PF 3 , PCl 3 , and PBr 3 . The electron-rich (PR 3 ) 2 Pd fragments can act as Lewis bases towards the CO 2 molecule. We have examined the phosphine ligand influence on the electron density of the palladium center. In all cases the η 2 -C,O bonding mode was lowest in energy. The interaction between metal fragment and CO 2 frontier orbitals will be presented in order to provide an understanding of Pd-CO 2 bonding.

Stepwise Ethene and/or Methyl Acrylate/CO Insertions into the Pd-C Bond of Cationic Palladium(II) Complexes Stabilized by a (P,O) Chelate This work was supported by the Centre National de la Recherche Scientifique, the Ministère de l'Education Nationale, de l'Enseignement et de la Recherche (Grant to C.F. and Action Incitative), Elf Atochem, and Elf Aquitaine. Special thanks are due to Ms. N.

Early intermediates along the stepwise multi-insertions of CO, ethene, or methyl acrylate into the palladium–carbon bond of cationic palladium(II) complexes such as 1, which is stabilized by a P,O chelate, have been isolated under ambiant conditions. The crystallographically characterized CO–ethene coupling product 2 reversibly inserts further CO to give the isolated intermediate 3 (not shown), which affords 4 or 5 upon insertion of ethene or methyl acrylate, respectively.

Highly Chemoselective Hydrogenation with Retention of the Epoxide Function Using a Heterogeneous Pd/C-Ethylenediamine Catalyst and THF

In general, palladium-carbon (Pd/C) catalyzed hydrogenation of epoxides affords the corresponding primary and secondary alcohols as a mixture. It has been found that the catalytic activity of a Pd/C-ethylenediamine complex catalyst [Pd/C(en)] in the hydrogenolysis of epoxide functions is drastically reduced. Herein we describe a mild and chemoselective method for the hydrogenation of olefin, nitro, and azide functions with retention of the epoxide function. The chemoselectivity was accomplished by using a combination of 5 % Pd/C(en) and THF as solvent. A significant drop in the chemoselectivity of the hydrogenation is observed with 5 % Pd/C(en) in MeOH. These results reinforce the utility of epoxides as important precursors of alcohols in synthetic chemistry.