Résultat de la recherche
Ruthenium nanoparticles intercalated in hectorite: a reusable hydrogenation catalyst for benzene and toluene
The cationic organometallic aqua complexes formed by hydrolysis of [(C6H6)RuCl2]2 in water, mainly [(C6H6)Ru(H2O)3]2+, intercalate into sodium hectorite by ion exchange, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in ethanol with mol. hydrogen (50 bar, 100°) with decompn. of the organometallic aqua complexes to give a black material, in which ruthenium(0) nanoparticles (9-18 nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. The black ruthenium-modified hectorite efficiently catalyzes the hydrogenation of benzene and toluene in ethanol (50 bar H2, 50°), the turnover frequencies attaining 7000 catalytic cycles per h. [on SciFinder(R)]
Supramolecular cluster catalysis: facts and problems
By checking the chem. underlying the concept of supramol. cluster catalysis the authors identified two major errors in their publications related to this topic, which are essentially due to contamination problems. (1) The conversion of the closed cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ (1) into the open cluster cation [H2Ru3(C6H6)(C6Me6)2(O)(OH)]+ (2), which the authors had ascribed to a reaction with H2O in the presence of ethylbenzene is simply an oxidn. reaction which occurs in the presence of air. (2) The higher catalytic activity obsd. with ethylbenzene, which the authors had erroneously attributed to the open cluster cation 2, was due to the formation of RuO2·nH2O, caused by a hydroperoxide contamination present in ethylbenzene. [on SciFinder(R)]
Ruthenium Nanoparticles Intercalated in Hectorite: A Reusable Hydrogenation Catalyst for Benzene and Toluene
The cationic organometallic aqua complexes formed by hydrolysis of [(C6H6)RuCl2]2 in water, mainly [(C6H6)Ru(H2O)3]2+, intercalate into sodium hectorite by ion exchange, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in ethanol with molecular hydrogen (50 bar, 100°C) with decomposition of the organometallic aqua complexes to give a black material, in which ruthenium(0) nanoparticles (9–18 nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. The black ruthenium-modified hectorite efficiently catalyses the hydrogenation of benzene and toluene in ethanol (50 bar H2, 50°C), the turnover frequencies attaining 7000 catalytic cycles per hour.
Supramolecular cluster catalysis : facts and problems
By checking the chemistry underlying the concept of "supramolecular cluster catalysis" we identified two major errors in our publications related to this topic, which are essentially due to contamination problems. (1) The conversion of the "closed" cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ (1) into the "open" cluster cation [H2Ru3(C6H6)(C6Me6)2 (O)(OH)]+ (2), which we had ascribed to a reaction with water in the presence of ethylbenzene is simply an oxidation reaction which occurs in the presence of air. (2) The higher catalytic activity observed with ethylbenzene, which we had erroneously attributed to the "open" cluster cation [H2Ru3(C6H6)(C6Me6)2(O)(OH)]+ (2), was due to the formation of RuO2• nH2O, caused by a hydroperoxide contamination present in ethylbenzene.
The water-soluble cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+: Improved synthesis, aerobic oxidation, electrochemical properties and ligand exchange studies
The synthesis of the trinuclear cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ (1) has been considerably improved by changes in the NaBH4 addition step and by introducing chromatographic methods; in addition, the redox and ligand exchange properties of 1 have been studied. Although exposure of an aqueous solution of 1 to air yields the oxidised cluster [H3Ru3(C6H6)(C6Me6)2(O) (OH)]+ (2), cyclic voltammetry of [1][BF4] in acetonitrile reveals a first reversible oxidation step that does not involve 2. Bulk electrolysis of 1 and 2 in the same medium affords only decomposition products. Ligand exchange in 1 takes place only at higher temperatures: by heating a mixture of toluene with an aqueous solution of [1][BF4] (1000:1) to 110 °C for 2 h, the formation of the toluene derivative [H3Ru3(C6H5Me)(C6Me6)2 (O)]+ (3) is observed in small quantities. H/D exchange of 1 with D2O does not occur up to 90 °C; however, in the presence of D2, H/D exchange with 1 is observed to give the deuterated derivative [D3Ru3 (C6H6)(C6Me6)2 (O)]+ (1a). The results provide an improved synthesis of 1, as well as information about its redox and ligand-exchange reactions, results necessary to understand and develop the chemistry of 1.
Mechanistic in situ High-Pressure NMR Studies of Benzene Hydrogenation by Supramolecular Cluster Catalysis with [(η6-C6H6)(η6-C6Me6)2Ru3(μ3-O)(μ2-OH)(μ2-H)2][BF4]
In situ high-pressure NMR spectroscopy of the hydrogenation of benzene to give cyclohexane, catalysed by the cluster cation [(η6-C6H6)(η6-C6Me6)2Ru3(μ3-O)(μ2-OH)(μ2-H)2]+2, supports a mechanism involving a supramolecular host-guest complex of the substrate molecule in the hydrophobic pocket of the intact cluster molecule.