CLÚSTERES MOLECULARES DE ORO, PALADIO Y COBRE COMO CATALIZADORES DE REACCIONES ORGÁNICAS

En la presente tesis doctoral se ha realizado un estudio sobre las especies catalíticamente activas en reacciones de formación de enlace carbono-carbono y carbono-heteroátomo catalizadas por oro, paladio y cobre. En el caso de las reacciones catalizadas por oro (sales de Au+ o Au3+ complejos de Au+ o nanopartículas de Au), se ha comprobado que, independientemente del catalizador de oro de partida, las especies catalíticamente activas en algunas reacciones son clústeres atómicos de oro de entre 2 y 9 átomos, y que, dentro de este rango, las reacciones son sensibles al número de átomos de oro que forman el clúster. Estos clústeres presentan una actividad catalítica inusualmente alta para este tipo de reacciones, llegando a realizar hasta 10 millones de ciclos catalíticos por hora a temperatura ambiente. Además, se ha estudiado la estabilidad de estos clústeres frente a aniones y ligandos en disolución. En el caso de las reacciones de acoplamiento cruzado catalizadas por paladio bajo condiciones de Jeffery (sin ligandos, amida como disolvente, 130-140 oC), se ha observado la formación y actividad catalítica de clústeres de Pd de entre 3 y 4 átomos para las reacciones de acoplamiento de Heck, Sonogashira, Stille y Suzuki. Estos clústeres se estabilizan en presencia de agua o aminas y presentan una alta actividad catalítica para yoduros y bromuros de arilo. También se ha observado la formación de clústeres de Cu en reacciones de acoplamiento entre yoduros de arilo y diversos nucleófilos (amidas, fenoles, fosfinas, tioles, alquinos) en ausencia de ligandos diamina. Además, se ha podido establecer la naturaleza, mecanismo de formación y cantidad de estos clústeres de Cu formados a partir de una sal de partida. Por último, se ha comparado la actividad catalítica de los clústeres de oro, paladio y cobre para reacciones tipo donde se necesita catálisis Lewis, radicalaria o red-ox, pudiendo relacionar la naturaleza fisicoquímica de los clústeres con su actividad catalítica.Oliver Meseguer, J. (2015). CLÚSTERES MOLECULARES DE ORO, PALADIO Y COBRE COMO CATALIZADORES DE REACCIONES ORGÁNICAS [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48566TESISPremios Extraordinarios de tesis doctorale

Nanotitania catalyzes the chemoselective hydration and alkoxylation of epoxides

[EN] Glycols and ethoxy- and propoxy-alcohols are fundamental chemicals in industry, with annual productions of millions of tons, still manufactured in many cases with corrosive and unrecoverable catalysts such as KOH, amines and BF3 center dot OEt2. Here we show that commercially available, inexpensive, non-toxic, solid and recyclable nanotitania catalyzes the hydration and alkoxylation of epoxides, with water and primary and secondary alcohols but not with phenols, carboxylic acids and tertiary alcohols. In this way, the chemoselective synthesis of different glycols and 1,4-dioxanones, and the implementation of nanotitania for the production in-flow of glycols and alkoxylated alcohols, has been achieved. Mechanistic studies support the key role of vacancies in the nano-oxide catalyst.A.L.-P. thanks the MICIIN (project code PID2020-115100GB-I00) for financial support. J.O.-M. thanks the Juan de la Cierva Program for the concession of a contract (IJC2018-036514-I). J.B.-S. thanks La Caixa Foundation grant (ID 100010434), code LCF/BQ/DI19/11730029.Oliver-Meseguer, J.; Ballesteros-Soberanas, J.; Tejeda-Serrano, M.; Martínez-Castelló, A.; Leyva Perez, A. (2021). Nanotitania catalyzes the chemoselective hydration and alkoxylation of epoxides. Molecular Catalysis. 515:1-11. https://doi.org/10.1016/j.mcat.2021.111927S11151

Hydrogen migration at restructuring palladium-silver oxide boundaries dramatically enhances reduction rate of silver oxide.

Heterogeneous catalysts are complex materials with multiple interfaces. A critical proposition in exploiting bifunctionality in alloy catalysts is to achieve surface migration across interfaces separating functionally dissimilar regions. Herein, we demonstrate the enhancement of more than 104 in the rate of molecular hydrogen reduction of a silver surface oxide in the presence of palladium oxide compared to pure silver oxide resulting from the transfer of atomic hydrogen from palladium oxide islands onto the surrounding surface formed from oxidation of a palladium-silver alloy. The palladium-silver interface also dynamically restructures during reduction, resulting in silver-palladium intermixing. This study clearly demonstrates the migration of reaction intermediates and catalyst material across surface interfacial boundaries in alloys with a significant effect on surface reactivity, having broad implications for the catalytic function of bimetallic materials

Generation and Reactivity of Electron-Rich Carbenes on the Surface of Catalytic Gold Nanoparticles

[EN] The reactive nature of carbenes can be modulated, and ultimately reversed, by receiving additional electron density from a metal. Here, it is shown that Au nanoparticles (NPs) generate an electron-rich carbene on surface after transferring electron density to the carbonyl group of an in situ activated diazoacetate, as assessed by Fourier transformed infrared (FT¿IR) spectroscopy, magic angle spinning nuclear magnetic resonance (MAS NMR), and Raman spectroscopy. Density functional theory (DFT) calculations support the observed experimental values and unveil the participation of at least three different Au atoms during carbene stabilization. The surface stabilized carbene shows an extraordinary stability against nucleophiles and reacts with electrophiles to give new products. These findings showcase the ability of catalytic Au NPs to inject electron density in energetically high but symmetrically allowed valence orbitals of sluggish molecules.Financial support by MINECO through the Severo Ochoa program, RETOS program (CTQ2014-55178-R), and Ramon y Cajal Program (to A.L.-P.) is acknowledged. J.O.-M. thanks ITQ for the concession of a contract. We are thankful for the electron microscopy service of UPV.Oliver-Meseguer, J.; Boronat Zaragoza, M.; Vidal Moya, JA.; Concepción Heydorn, P.; Rivero-Crespo, MÁ.; Leyva Perez, A.; Corma Canós, A. (2018). Generation and Reactivity of Electron-Rich Carbenes on the Surface of Catalytic Gold Nanoparticles. Journal of the American Chemical Society. 140(9):3215-3218. https://doi.org/10.1021/jacs.7b13696S32153218140

Soluble/MOF-Supported Palladium Single Atoms Catalyze the Ligand-, Additive-, and Solvent-Free Aerobic Oxidation of Benzyl Alcohols to Benzoic Acids

Metal single-atom catalysts (SACs) promise great rewards in terms of metal atom efficiency. However, the requirement of particular conditions and supports for their synthesis, together with the need of solvents and additives for catalytic implementation, often precludes their use under industrially viable conditions. Here, we show that palladium single atoms are spontaneously formed after dissolving tiny amounts of palladium salts in neat benzyl alcohols, to catalyze their direct aerobic oxidation to benzoic acids without ligands, additives, or solvents. With this result in hand, the gram-scale preparation and stabilization of Pd SACs within the functional channels of a novel methyl-cysteine-based metal-organic framework (MOF) was accomplished, to give a robust and crystalline solid catalyst fully characterized with the help of single-crystal X-ray diffraction (SCXRD). These results illustrate the advantages of metal speciation in ligand-free homogeneous organic reactions and the translation into solid catalysts for potential industrial implementation.This work was supported by the Ministero dell’Istruzione, dell’Università e della Ricerca (Italy) and the MINECO (Spain) (Projects PID2019−104778GB−I00, CTQ 2017–86735–P, RTC–2017–6331–5, Severo Ochoa program SEV–2016–0683 and Excellence Unit “Maria de Maeztu” CEX2019−000919−M). E.T. and M.M. thank MINECO and ITQ for the concession of a contract. D.A. acknowledges the financial support of the Fondazione CARIPLO/“Economia Circolare: ricerca per un futuro sostenibile” 2019, Project code: 2019–2090, MOCA and Diamond Light Source for awarded beamtime and provision of synchrotron radiation facilities and thanks Dr. Sarah Barnett and David Allan for their assistance at I19 beamline (Proposal No. MT18768-1). Thanks are also extended to the “2019 Post-doctoral Junior Leader-Retaining Fellowship, la Caixa Foundation (ID100010434 and fellowship code LCF/BQ/PR19/11700011” (J.F.-S.) and “La Caixa” scholarship (ID 100010434) LCF/BQ/DI19/11730029 (J.B.-S). E.P. acknowledges the financial support of the European Research Council under the European Union’s Horizon 2020 research and innovation programme/ERC Grant Agreement No 814804, MOF reactors. J.O.-M. acknowledges the Juan de la Cierva program for the concession of a contract (IJC2018-036514-I). We gratefully acknowledge to ALBA synchrotron for allocating beamtime and CLÆSS beamline staff for their technical support during our experiment. The computations were performed on the Tirant III cluster of the Servei d’Informàtica of the University of Valencia.Peer reviewe

Regioirregular and catalytic Mizoroki-Heck reactions

[EN] The palladium-catalysed cross-coupling reaction between alkenes and aryl halides (the Mizoroki-Heck reaction) is a powerful methodology to construct new carbon-carbon bonds. However, the success of this reaction is in part hampered by an extremely marked regioselectivity on the double bond, which dictates that electron-poor alkenes react exclusively on the beta-carbon. Here, we show that ligand-free, few-atom palladium clusters in solution catalyse the alpha-selective intramolecular Mizoroki-Heck coupling of iodoaryl cinnamates, and mechanistic studies support the formation of a sterically encumbered cinnamate-palladium cluster intermediate. Following this rationale, the alpha-selective intermolecular coupling of aryl iodides with styrenes is also achieved with palladium clusters encapsulated within fine-tuned and sterically restricted zeolite cavities to produce 1,1-bisarylethylenes, which are further engaged with aryl halides by a metal-free photoredox-catalysed coupling. These ligand-free methodologies significantly expand the chemical space of the Mizoroki-Heck coupling.This work was supported by MINECO (Spain, projects CTQ 2017-86735-P, PID2019-105391GB-C22 and MAT2017-82288-C2-1-P, Severo Ochoa programme SEV-2016-0683 and the Juan de la Cierva programme). F.G.-P. and R.G. thank ITQ for the concession of a contract. J.O.-M. acknowledges the Juan de la Cierva programme for the concession of a contract, and R.P.-R. and J.C.-S. thank the Plan GenT programme (CIDEGENT/2018/044) funded by Generalitat Valenciana. HR STEM measurements were performed at DME-UCA in Cadiz University, with financial support from FEDER/MINECO (PID2019-110018GA-I00 and PID2019-107578GA-I00). We acknowledge ALBA Synchrotron for allocating beamtime and CL AE SS beamline staff for their technical support during our experiment.Garnes-Portoles, F.; Greco, R.; Oliver-Meseguer, J.; Castellanos-Soriano, J.; Jiménez Molero, MC.; Lopez-Haro, M.; Hernández-Garrido, JC.... (2021). Regioirregular and catalytic Mizoroki-Heck reactions. Nature Catalysis. 4(4):293-303. https://doi.org/10.1038/s41929-021-00592-3S2933034

Reactivity of Electron-Deficient Alkynes on Gold Nanoparticles

[EN] Propiolates cyclotrimerize in the presence of catalytic amounts of gold nanoparticles to give aryl benzoates in high yields and with turnover frequencies of thousands per hour. Types of alkynes other than propiolates do not react, and, if molecular oxygen is present and dissociated by the gold nanoparticles, electron-rich arenes engage with the propiolate to form a new C–C bond. The activation of propiolates and electron-rich arenes to form C–C bonds, beyond gold-catalyzed Michael additions, constitutes a new example of how and where gold nanoparticles modify the electronic density of unsaturated C–C bonds and opens the door to future transformations.A.L.-P. thanks CSIC for a contract. J.O.-M. thanks ITQ for a postgraduate scholarship. J.R.C.-A. and P.R.-M. thank MECD for the concession of a FPU contract. Financial support by the Severo Ochoa program and Consolider-Ingenio 2010 (proyecto MULTICAT) from MICIINN is acknowledged, and also the King Saud University. P.S. thanks European Union Seventh Framework programme (PIOF-GA-2009-253129).Leyva Perez, A.; Oliver Meseguer, J.; Cabrero Antonino, JR.; Rubio Marqués, P.; Serna, P.; Al-Resayes, SI.; Corma Canós, A. (2013). Reactivity of Electron-Deficient Alkynes on Gold Nanoparticles. ACS Catalysis. 3(8):1865-1873. https://doi.org/10.1021/cs400362cS186518733