pinecone/core-2020-05-10-deduplication huggingface dataset:
N-Heterocyclic Carbenes Supported on Vinylic Addition Polynorbornene: A Recyclable and Recoverable Organocatalyst

Producción CientíficaA bromoalkyl functionalized vinylic addition polynorbornene has been used as an inert new scaffold to support imidazolium salts by straightforward nucleophilic substitution using different imidazoles ImR (R=Me, mesityl, 2,6-iPr2C6H3). These polymers, VA-PNB-(CH2)4ImRBr, are precursors of N-heterocyclic carbenes which are useful as heterogeneous organocatalysts. The polymeric carbenes have been tested in two model reactions: The synthesis of saturated esters from α,β-unsaturated aldehydes and the conjugate umpolung reaction of α,β-unsaturated aldehydes for the synthesis of γ-butyrolactones. The supported catalyst (R=mesityl) is fully recyclable and can be recovered as an imidazolium salt and stored for further use.Ministerio de Economía, Industria y Competitividad (CTQ2013-48406-P)Ministerio de Economía, Industria y Competitividad (CTQ2010-18901/BQU)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13
Hydrofluorination of alkynes catalysed by gold bifluorides

The ERC (Advanced Investigator Award FUNCAT and PoC award GOLDCAT), the EPSRC and Syngenta are gratefully acknowledged for support of this work. Umicore AG is acknowledged for their generous gift of auric acid. S.P.N. is a Royal Society Wolfson Research Merit Award holder.We report the synthesis of nine new N-heterocyclic carbene gold bifluoride complexes starting from the corresponding N-heterocyclic carbene gold hydroxides. A new methodology to access N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) fluoride starting from N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) hydroxide and readily available potassium bifluoride is also reported. These gold bifluorides were shown to be efficient catalysts in the hydrofluorination of symmetrical and unsymmetrical alkynes, thus affording fluorinated stilbene analogues and fluorovinyl thioethers in good to excellent yields with high stereo- and regioselectivity. The method is exploited further to access a fluorinated combretastatin analogue selectively in two steps starting from commercially available reagents.Publisher PDFPeer reviewe
Selective oxidation of salicylic alcohol to aldehyde with O2/H2 using Au-Pd on titanate nanotubes catalysts

Alcohol oxidation with 100% selectivity to the aldehyde product (versus acid formation) is achieved at mild conditions by a tandem-type system where the intermediate species of hydrogen peroxide formation from an O2/H2 mixture are formed and utilised directly over Au-Pd/Ti-NT catalysts. Insitu reaction of the intermediate species minimises the parallel decomposition of hydrogen peroxide into water, overcoming one of the limitations on the use of hydrogen peroxide as a green oxidant. In the mix for selective oxidation: Insitu formation and utilisation of intermediate oxidising species from O2/H2 mixtures in a tandem-type system minimises the parallel decomposition of hydrogen peroxide with 100% selectivity to the aldehyde product
Palladium and Bimetallic Palladium–Nickel Nanoparticles Supported on Multiwalled Carbon Nanotubes: Application to Carbon–Carbon Bond-Forming Reactions in Water

Palladium and bimetallic Pd–Ni nanoparticles (NPs) protected by polyvinylpyrrolidone were prepared by the reduction-by-solvent method and deposited on multiwalled carbon nanotubes (MWCNTs). The catalytic activity of these NPs to carbon–carbon bond-forming reactions was studied by using 0.1 mol % Pd loading, at 120 °C for 1 h and water as a solvent under ligand-free conditions. The Suzuki–Miyaura reaction took place quantitatively for the cross-coupling of 4-bromoanisole with phenylboronic acid, better than those obtained with potassium phenyltrifluoroborate, with Pd50Ni50/MWCNTs as a catalyst and K2CO3 as a base and TBAB as an additive, with good recyclability during 4 cycles with some Ni leaching. The Hiyama reaction of 4-iodoanisole with trimethoxyphenylsilane, under fluoride-free conditions using 50 % aqueous NaOH solution, was performed with Pd/MWCNTs as a catalyst in 83 % yield with low recyclability. For the Mizoroki-Heck reaction 4-iodoanisole and styrene gave the corresponding 4-methoxystilbene quantitatively with Pd50Ni50/MWCNTs using K2CO3 as a base and TBAB as an additive although the recycle failed. In the case of the Sonogashira-Hagihara reaction, Pd/MWCNTs had to be used as a catalyst and pyrrolidine as a base for the coupling of 4-iodoanisole with phenylacetylene under copper-free conditions. The corresponding 4-methoxytolane was quantitatively obtained allowing the recycling of the catalyst during 3 cycles.The Spanish Ministerios de Ciencia e Innovación (MICINN) and Economía y Competitividad (MINECO) (projects CTQ 2007-62771/BQU, CTQ2010-20387, CTQ2013-43446-P, Consolider Ingenio 2010, CSD2007-00006, CTQ2014-51912-REDC, CTQ2012-31762 and RyC-2009-03813 fellowship), FEDER, the Generalitat Valenciana (PROMETEO 2009/039, PROMETEOII/2014/010, and PROMETEOII/2014/017) and the University of Alicante are gratefully acknowledged for financial support
Para-quinone methide: A new player in asymmetric catalysis

This is the accepted version of the following article: Parra, A. and Tortosa, M. (2015), para-Quinone Methide: a New Player in Asymmetric Catalysis. ChemCatChem, 7: 1524–1526, which has been published in final form at http://dx.doi.org/10.1002/cctc.201500176. This article may be used for non-commercial purposes in accordance with the Wiley Self-Archiving Policy wiley.com/WileyCDA/Section/id- 820227.htmlWe thank the European Research Council (ERC-337776) for the financial support. M. T. and A. P. thank MICINN for RyC and JdC contracts, respectivel
Suzuki-Miyaura diversification of amino acids and dipeptides in aqueous media

The authors gratefully acknowledge the IWT Flanders and Janssen Pharmaceutica for financial support of T.W. This work is supported by the Scientific Research Network (WOG) “Sustainable chemistry for the synthesis of fine chemicals” of the Research Foundation - Flanders (FWO).The Suzuki-Miyaura derivatisation of free amino acids, peptides and proteins is an attractive area with much potential utility for medicinal chemistry and chemical biology. Here we report the modification of unprotected and Boc-protected aromatic amino acids and dipeptides in aqueous media, enabling heteroarylation and vinylation. We systematically investigate the impact of the peptide backbone and adjacent amino acid residues upon the reaction. Our studies reveal that whilst asparagine and histidine hinder the reaction, by utilising dppf, a ferrocene-based bidentate phosphine ligand, cross-coupling of halophenylalanine or halotryptophan adjacent to such a residue could be enabled. Our studies reveal dppf to have good compatibility with all unprotected, proteinogenic amino acid side chains.PostprintPeer reviewe
Improved stability of Pd/Al2O3 prepared from palladium nanoparticles protected with carbosilane dendrons in the dimethyl ether steam reforming reaction

The dimethyl ether steam reforming reaction to generate hydrogen was tested over 1wt% Pd/Al2O3 catalysts prepared from different precursors. The conventional catalyst prepared by incipient wetness impregnation from palladium nitrate underwent strong deactivation under reforming conditions at 823K because of metal sintering and carbon deposition. The same occurred over the catalyst prepared from preformed Pd nanoparticles protected with dodecanethiol. In contrast, catalysts prepared from Pd nanoparticles protected with carbosilane dendrons showed enhanced stability and good performance for the production of hydrogen. This was because of the formation of SiO2 at the Pd-Al2O3 interface that acted as a pinning center and prevented Pd migration under the reaction conditions as well as the accumulation of carbon.Postprint (author's final draft
Importance of the Support Properties for Immobilization or Purification of Enzymes

Immobilization and purification of enzymes are usual requirements for their industrial use. Both purification and immobilization have a common factor: they use a solid activated support. Using a support for enzyme purification means having mild conditions for enzyme release and a selective enzyme–support interaction is interesting. When using a support for immobilization, however, enzyme desorption is a problem. The improvement of enzyme features through immobilization is a usual objective (e.g., stability, selectivity). Thus, a support designed for enzyme purification and a support designed for enzyme immobilization may differ significantly. In this review, we will focus our attention on the requirements of a support surface to produce the desired objectives. The ideal physical properties of the matrix, the properties of the introduced reactive groups, the best surface activation degree to reach the desired objective, and the properties of the reactive groups will be discussed.We gratefully recognize the support from the Spanish Government, CTQ2013-41507-R, Colciencia (Colombia) and CNPq (Brazil). The predoctoral fellowships for Mr dos Santos (CNPq, Brazil) are also recognized. Á. Berenguer-Murcia thanks the Spanish Ministerio de Ciencia e Innovaciûn for a Ramón y Cajal fellowship (RyC-2009-03813)
Influence of different palladium precursors on the properties of solution-combustion-synthesized palladium/ceria catalysts for methane combustion

A series of Pd/CeO2 catalysts was prepared by solution combustion synthesis (SCS) using different Pd precursors. The powders were characterized by complementary techniques such as BET surface area measurements, X-Ray diffraction analysis, X-Ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxidation, and high-resolution TEM. The results obtained evidenced the formation of a Pd-Ce solid solution on all SCS samples. This solid solution is in the form of an ordered supercell structure only in the SCS catalyst prepared from palladium nitrate. This was correlated to the heat of reaction between Pd(NO3)(2) and the fuel. The samples were tested for methane catalytic combustion, and the reaction rates on all SCS samples were approximately twice that of the impregnated counterpart, irrespective of the precursor. This was attributed to the presence of the Pd-O-Ce solid solution, which gave rise to strong Pd-ceria interactions.Postprint (author's final draft
Unprecedented comonomer dependence of the stereochemistry control in Pd-catalyzed CO/vinyl arene polyketone synthesis

Two pyrene-tagged iminopyridines (N-N') were used to synthesize neutral and monocationic, palladium(II) complexes, [Pd(Me)Cl(N-N')] and [Pd(Me)(MeCN)(N-N')][PF6]. The monocationic complexes generated active catalysts in the CO/vinyl arene copolymerization leading to polyketones with yields and molecular weight strongly dependent on N-N', being the ketimine catalysts one order of magnitude more productive than the aldimine counterpart. The stereochemistry of polyketones synthesized with the aldimine catalyst was found to be dependent on the vinyl comonomer: prevailingly syndiotactic copolymers were obtained for styrene, prevailingly isotactic copolymers were produced for 4-methyl styrene, and atactic macromolecules were formed for the 4-tbutyl styrene. The statistical analysis demonstrated that the control of the stereochemistry switched from enantioselective site control for 4-methyl styrene to a combination of chain-end and enantioselective site control for styrene
Noninvasive Nanoscopy Uncovers the Impact of the Hierarchical Porous Structure on the Catalytic Activity of Single Dealuminated Mordenite Crystals

Spatial restrictions around catalytic sites, provided by molecular-sized micropores, are beneficial to reaction selectivity but also inherently limit diffusion. The molecular transport can be enhanced by introducing meso- and macropores. However, the impact of this extraframework porosity on the local nanoscale reactivity is relatively unexplored. Herein we show that the area of enhanced reactivity in hierarchical zeolite, examined with super-resolution fluorescence microscopy, is spatially restricted to narrow zones around meso- and macropores, as observed with focused ion-beam-assisted scanning electron microscopy. This comparison indicates that reagent molecules efficiently reach catalytic active sites only in the micropores surrounding extraframework porosity and that extensive macroporosity does not warrant optimal reactivity distribution throughout a hierarchical porous zeolite.status: publishe
α-Methylenation of methyl propanoate via catalytic dehydrogenation of methanol

A one-pot system for the conversion of methyl propanoate (MeP) to methyl methacrylate (MMA) has been investigated. In particular, this study is focused on the possibility of performing catalytic dehydrogenation of methanol for the in situ production of anhydrous formaldehyde, which is then consumed in a one-pot base-catalysed condensation with MeP to afford methyl 3-hydroxy-2-methylpropanoate, which spontaneously dehydrogenates to MMA, some of which is subsequently hydrogenated to methyl 2-methypropanoate (MiBu).PostprintPostprintPeer reviewe
Enzyme-modified particles for selective biocatalytic hydrogenation by hydrogen-driven NADH recycling

We describe a new approach to selective H-2-driven hydrogenation that exploits a sequence of enzymes immobilised on carbon particles. We used a catalyst system that comprised alcohol dehydrogenase, hydrogenase and an NAD(+) reductase on carbon black to demonstrate a greater than 98% conversion of acetophenone to phenylethanol. Oxidation of H-2 by the hydrogenase provides electrons through the carbon for NAD(+) reduction to recycle the NADH cofactor required by the alcohol dehydrogenase. This biocatalytic system operates over the pH range 6-8 or in un-buffered water, and can function at low concentrations of the cofactor (10m NAD(+)) and at H-2 partial pressures below 1bar. Total turnover numbers >130000 during acetophenone reduction indicate high enzyme stability, and the immobilised enzymes can be recovered by a simple centrifugation step and re-used several times. This offers a route to convenient, atom-efficient operation of NADH-dependent oxidoreductases for selective hydrogenation catalysis.EC/FP7/258600/EU/Understanding and Exploiting Biological Catalysts for Energy Cycling: Development of Infrared Spectroelectrochemistry for Studying Intermediates in Metalloenzyme Catalysis/EnergyBioCatalysisEC/FP7/297503/EU/Modular beads for regeneration of bio-cofactors in enzyme-catalysed synthesis/HydRegenDFG, EXC 314, Unifying Concepts in Catalysi
Light-stable silver N-Heterocyclic carbene catalysts for the alkynylation of ketones in air

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C) for funding.N-Heterocyclic carbene (NHC) silver(I) complexes were efficiently employed in the alkynylation of ketones. These cationic complexes were found highly active and efficient under mild conditions without the need of additive, and in air. The mechanism of this transformation was investigated. Experiments suggest the formation of a silver-acetylide key intermediate and the release of one ligand from the silver centre enabling the transformation.PostprintPeer reviewe
Iron Oxide Nanoparticles Modified with Carbon Quantum Nanodots for the Stabilization of Palladium Nanoparticles: An Efficient Catalyst for the Suzuki Reaction in Aqueous Media under Mild Conditions

Magnetic Fe3O4 nanoparticles (NPs) functionalized with carbon dots (C-dots) that contain carboxylic acid and hydroxyl groups were synthesized successfully and used for the reduction of PdII and the formation of Pd NPs. The new material was characterized by SEM, TEM, energy-dispersive spectroscopy, solid UV spectroscopy, vibrating sample magnetometry, XRD, and X-ray photoelectron spectroscopy and was used as a very efficient catalyst in the Suzuki–Miyaura cross-coupling reaction of aryl bromides and chlorides with arylboronic acids in aqueous media. Design of experiments indicates that the use of 0.22 mol % of Pd, K2CO3 as the base, and aqueous ethanol are the best reaction conditions. The reactions of aryl bromides take place at room temperature, and aryl chlorides react at 80 °C. The easily synthesized and air-stable catalyst Pd@C-dots@Fe3O4 NPs could be separated from the reaction mixture by using an external magnet and reused in eight consecutive runs with no significant loss of catalytic activity.The authors are grateful to the Institute for Advanced Studies in Basic Sciences (IASBS) and the Iran National Science Foundation (INSF-Grant number of 94010666) for support of this work. C.N. is grateful to the Spanish Ministerio de Economia y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), FEDER, the Generalitat Valenciana (PROMETEOII/2014/017), and the University of Alicante for financial support
Synthesis of bifunctional monomers by the palladium-catalyzed carbonylation of cardanol and its derivatives

The authors thank the Royal Society Leverhulme Africa Program for funding this project.A 1,2-bis(di-tert-butylphosphinomethyl)benzene-modified palladium catalyst has been used to synthesize bifunctional monomers of different chain lengths from cardanol. Short-chain derivatives of cardanol, such as (E)-3-(dodec-8-enyl)phenol; HOPhC12-ene, (E)-3-(undec-8-enyl)phenol; HOPhC11-ene, (E)-3-(dec-8-enyl)phenol; HOPhC10-ene, and 3-(non-8-enyl)phenol; HOPhC9-ene, were synthesized by the metathesis of cardanol with symmetrical internal alkenes. These derivatives were methoxycarbonylated to produce monomers with different chain lengths such as methyl-16-(3-hydroxyphenyl)hexadecanoate; HOPhC15COOMe, methyl-13-(3-hydroxyphenyl)tridecanoate; HOPhC12COOMe, methyl-12-(3-hydroxyphenyl)dodecanoate; HOPhC11COOMe, methyl-11-(3-hydroxyphenyl)undecanoate; HOPhC10COOMe, and methyl-10-(3-hydroxyphenyl)decanoate; HOPhC9COOMe, respectively. Polymerization of the synthesized monomers produced oligomers that consist of up to seven monomer units as confirmed by MALDI-TOF-MS. Lactone formation was also observed in some cases under polymerization conditions.PostprintPostprintPeer reviewe
InSitu FTIR Spectroscopy: Probing the Electrochemical Interface during the Oxygen Reduction Reaction on a Commercial Platinum High-Surface-Area Catalyst

Insitu observation of anion adsorption on industrial high-surface-area catalysts is used for the first time under oxygen reduction reaction (ORR) conditions with a defined mass transport. For this purpose, a specially fabricated electrode is used for which the catalyst layer is spray-coated on top of a structured Au contact layer and applied to our recently developed insitu attenuated total reflectance FTIR wall-jet electrode. The designed interface allows us to track anion adsorption and measure the reaction rate simultaneously under mass controlled conditions. The observed absorption bands are caused by anion interaction with the active phase and also the carbon support. If we analyze the absorption band intensity of adsorbed anions as a function of the oxygen reduction reaction rate, the band intensity decreases with the onset of the ORR. This shows that ORR inhibition is a complex interplay between site blocking caused by anion adsorption and oxide formation
Alkali-Metal-Catalyzed Cross-Dehydrogenative Couplings of Hydrosilanes with Amines

We report the N−H/H−Si cross-dehydrogenative coupling (CDC) of hydrosilanes and amines with high conversion (>90 %) and chemoselectivity for the production of silazanes, using group 1 metal hexamethyldisilazides [MN(SiMe3)2] (M=Li, Na, K) as precatalysts under mild conditions. [KN(SiMe3)2] showed higher activity than the congeneric lithium and sodium salts. The catalyzed CDC reaction displays a broad substrate scope. Phenylsilane and diphenylsilane react with a number of amines under ambient conditions; more elevated temperature is required for triphenylsilane to undergo CDC reactions. The intermediate lithium complex [(THF)2Li-{N(SiHPh2)(Dipp)}] (1) has been isolated and characterized in an attempt to identify the operative reaction mechanism
Oxime-Derived Palladacycles: Applications in Catalysis

Phenone oxime-derived palladacycles are stable, easy to prepare, and an excellent source of three- and four-atom Pd clusters able to show excellent catalytic activity in most of the classical carbon–carbon bond forming reactions (Mizoroki–Heck, Matsuda–Heck, Suzuki–Miyaura, Stille, Kumada, Hiyama, Ullmann, Sonogashira, and Glasser), generally with better performance than Pd(OAc)2 or other Pd salts. Aryl iodides, bromides, chlorides, and imidazolyl sulfonates can be used as substrates not only in organic solvents but also in aqueous solvents including neat water. Appropriate choice of the general reaction conditions allow these C−C bond forming reactions to be performed efficiently. These palladacycles have been also used in carbonylations, several types of annulations, ketone arylations, C−H activation, oxime rearrangements, and behave as metalloenzymes in hydrolytic processes, among others. Not only dimer complexes can be used, but also monomer ones with an additional ligand as well as those supported on polymers, silica, and bearing ionic or fluorinated tags.The Spanish Ministerio de Ciencia e Innovación (MICINN) (projects BQ2001-0724, CTQ2004-00808, CTQ 2007-62771/BQU, Consolider Ingenio 2010, CSD2007-00006, CTQ2010-20387), Spanish Ministerio de Economia y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), FEDER, the Generalitat Valenciana (PROMETEO 2009/039 and PROMETEOII/2014/017), and the University of Alicante are gratefully acknowledged for financial support
Vinylic Addition Polynorbornene as a Support for N-Heterocyclic Carbene Palladium Complexes: Catalytic Activity in C–C Cross– Coupling Reactions

Producción CientíficaA vinylic addition polynorbornene (VA-PNB) functionalized with imidazolium groups can be used to synthesize a well-defined supported palladium carbene complex. This complex is a suitable precatalyst for Suzuki and Negishi cross coupling reactions, and it can be reused. A close look to how the catalysis work reveals that palladium aggregates form on the polymer surface after the first catalytic reaction. However, they are not easily washed out and serve as a source of a small amount of homogeneous palladium active species (about 0.1‰ mol) that are responsible for the catalysis. The recovered polymer can be reused several times although increased induction and reaction times are observed in consecutive uses from one run to the next. The reaction was followed up by in situ IR spectroscopy using the ν(C-Br) absorption of the electrophile, so there is no need of an additional functional group to apply this technique.2017-12-15Ministerio de Economía, Industria y Competitividad (CTQ2013-48406-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13