Silica-supported Z-selective Ru olefin metathesis catalysts

Under embargo until: 2022-01-17Recently reported thiolate-coordinated ruthenium alkylidene complexes show promise in Z-selective and stereoretentive olefin metathesis reactions. Herein we describe the immobilization of three Ru complexes containing a bulky aryl thiolate on mesostructured silica via surface organometallic chemistry. The applied methodology gives isolated catalytic sites homogeneously distributed on the silica surface. The catalytic results with two model substrates show comparable Z-selectivities to those of the homogeneous counterparts.acceptedVersio

Iridium(I)/N-Heterocyclic Carbene Hybrid Materials: Surface Stabilization of Low-Valent Iridium Species for High Catalytic Hydrogenation Performance

An Ir-I(NHC)-based hybrid material was prepared using a methodology which allowed the precise positioning and isolation of the Ir centers along the pore channels of a silica framework. The full characterization of the material by solid-state NMR spectroscopy showed that the supported Ir sites were stabilized by the silica surface, as low-coordinated single-site complexes. The material is extremely efficient for the hydrogenation of functional alkenes. The catalytic performance (TOF and TON) is one to two orders of magnitude higher than those of their molecular Ir analogues, and could be related to the prevention of the bimolecular deactivation of Ir complexes observed under homogeneous conditions

Synthèse de matériaux hybrides organophosphines mésostructures et application en catalyse

La fonctionnalisation des silices hexagonales et mésoporeuses (SBA-15 et SBA-3) a été réalisée par la formation de liaisons covalentes entre les espèces organiques et/ou organométalliques à greffer et la surface pour éviter leur lixiviation. Ceci a nécessité un changement dans la structure du ligand pour apporter des fonctions de type trialcoxysilane pouvant se condenser avec les silanols de la surface. Les précurseurs que nous avons immobilisés sont des ligands de type dicyclohéxyl diphénylphosphine et des complexes Rh-DIOP. Les matériaux hybrides ainsi obtenus ont été engagés soit dans la réaction de Suzuki-Miyaura, soit dans la réaction d hydrogénation asymétrique. Les caractérisations effectuées à chaque étape de synthèse (DRX, RMN MAS 13C, 29Si et 31P, FT-IR, isotherme d adsorption et de désorption d azote, ATG et analyse élémentaire) confirment la conservation de la structure hexagonale du matériau et l intégrité du ligand ou du complexe grefféThe fonctionnalisation of hexagonally and mesoporous silica (SBA-15 or SBA-3) has been realised due to covalently bonds between the organic and/or organometallic species for grafting, and the material surfaces to forbid their leaching. This approach requires a modification in the ligands structure in the aim to add functions as trialkoxysilane groups which can be condensed with the surface silanols. The precursors that we immobilised are: dicylohexyl diphenylphosphine ligand and Rh-DIOP complexes. The obtained hybrids materials have catalytic properties. They are engaged either in the Suzuki-Miyaura reaction or in the asymmetric hydrogenation one. The characterizations performed at each synthesis step (XRD, MAS NMR 13C, 29Si and 31P, FT-IR, adsorption-desorption of nitrogen, TGA and analysis of elements) confirm the conservation of the hexagonally and the mesoporous structure of the initial materials and certified the integrity of the grafted ligand/comlexeLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Asymmetric hydrogenation using wilkinson-type rhodium complexes immobilized onto mesoporous silicia.

International audienceHeterogeneous chiral catalysts based on the DIOP-Rh system were prepared by covalent immobilization onto SBA type silicas using two different strategies. In the first route, a chiral analogue of Wilkinson's catalyst, [Rh(diop)(PPh2(CH2)2Si(OCH2CH3)3)Cl], 2, was immobilized onto a SBA-15 surface via a classical post-grafting procedure affording [2]/SBA-15. The covalent link to the surface was introduced through the monodentate phosphine ligand while keeping the structure of the chiral directing group intact. The second approach involved a two step synthesis: achiral RhCl{PPh2(CH2)2Si(OCH2CH3)3}3, 3, was first integrated within the walls of the silica framework during the synthesis of the oxide followed by incorporation of the chiral auxiliary in the pores of the material by post-synthetic grafting of a siloxane-containing DIOP ligand, 4. This led initially to the formation of [3][4]@PMOs in which stereogenic and reactive centers are not directly linked together but are in close proximity within a confined space. For characterisation, both molecular and solid state techniques were used to determine the structural and textural properties of the hybrid materials. The catalytic performances of the materials was evaluated using the hydrogenation of methyl (Z)-2-N-acetylaminocinnamate. Generally, the [2]/SBA-15catalyst leads to full, selective conversion with an ee of 57% in favor of the (R)-enantiomer. These data compare favorably to those reported for homogeneous counterparts. Rate of hydrogenation was further improved by varying the reaction parameters (temperature and pressure) or by generating in situ cationic active site just prior to the catalysis. In the case of [3][4]@PMOs, lower conversions were achieved (15 to 41%), which is attributed to restricted accessibility to the rhodium centre. Enantioinduction up to 26% was observed for these systems. Catalyst recycling was studied for [2]/SBA-15 and it was shown that the catalyst could be re-used several times without loss of enantioselectivity or activity

Suzuki–Miyaura Reactions of Aryl Chloride Derivatives with Arylboronic Acids using Mesoporous Silica-Supported Aryldicyclohexylphosphine

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Immobilization of chiral cationic diphosphine rhodium complexes in nanopores of mesoporous silica and application in asymmetric hydrogenation.

International audienceHeterogeneous chiral cationic rhodium complexes bearing bidentate phosphine derived from (−)-2,2-dimethyl-4,5-bis(diphenylphosphino)methyl)-1,3-dioxolane (DIOP) were prepared by covalent immobilization onto SBA type silica. In order to introduce the tether to the surface, it was necessary to modify chemically the DIOP ligand through a reaction sequence consisting of hydrolysis and condensation with organosiloxane precursor. Two types of cationic rhodium hybrid materials based on SBA-15 and partially capped SBA-3 type silica were prepared under classical grafting procedures. The catalytic solids were fully characterized using a wide variety of molecular and solid-state techniques to determine their structural and textural properties. The performances of these latter were then evaluated in the hydrogenation of methyl (Z)-2-N-acetylaminocinnamate under various reaction conditions (pressure and temperature). Generally, the activity of supported catalysts was high as full conversions were obtained but immobilization of the system leads to significant loss of enantioselectivity. The best ee (20%) was observed in the case of the catalyst whose surface had been passivated prior to the grafting but the enantiomeric excesses were fairly below the values of the homogeneous catalysis

Pt nanoparticles immobilized in mesostructured silica: a non-leaching catalyst for 1-octene hydrosilylation

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Active and Recyclable Polyethylene-Supported Iridium-(N-Heterocyclic Carbene) Catalyst for Hydrogen/Deuterium Exchange Reactions

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Supported Ru olefin metathesis catalysts via a thiolate tether

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