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Supramolecular cluster catalysis: Benzene hydrogenation catalyzed by a cationic triruthenium cluster under biphasic conditions
Supramolecular Cluster Catalysis : Benzene Hydrogenation Catalyzed by a Cationic Triruthenium Cluster under Biphasic Conditions
Reactions of the cluster anion [HRu3(CO)(11))](-) with dicyclohexylphosphine: Synthesis and molecular structure of H2Ru3(CO)(8)(PCy2)(2) and H2Ru3(CO)(6)(PCy2)(2)(HPCy2)(2)
The cluster anion [HRu3(CO)(11)](-) (1) reacts with dicyclohexylphosphine in THF solution to give the anionic derivative [HRu3(CO)(8)(PCy2)(2)](-) (2), protonation of which yields the neutral cluster H2Ru3(CO)(8)(PCy2)(2) (3) and, in the presence of excess phosphine, HRu3(CO)(7)(PCy2)(3) (4). In protic methanol as reaction medium, the reaction of 1 with HPCy2 gives directly the neutral complex H2Ru3(CO)(6)(PCy2)(2)(HPCy2)(2) (5). together with 4. The single-crystal structure X-ray analysis of 3 shows a closed triangular Ru, framework. Tho electron count is in accordance with the EAN rule, but the structure analysis of 5 reveals an open, almost linear Ru, skeleton, which is electron-deficient with respect to the EAN rule.
Mechanistic
In situ high-pressure NMR spectroscopy of the hydrogenation of benzene to give cyclohexane, catalysed by the cluster cation [(eta(6)-C6H6) (eta(6)-C6Me6)(2)Ru-3(mu(3)-O)(mu(2)-OH)(mu(2)-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.
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.
Reactions of the cationic complex [(eta(5)-C5Me5)(2)Ir-2(mu(2)-H)(3)](+) with nitrogen-containing heterocycles in aqueous solution
The dinuclear cation [(eta (5)-C5Me5)(2)Ir2(mu (2)-H)(3)](+) (1) reacts in aqueous solution with pyrazole and 4-methylpyrazole to give the bispyrazolato complexes [(eta (5)-C5Me5)(2)Ir-2(mu (2)-H)(mu (2)-eta (1),eta (1)-N2C3H2R)(2)](+) (R = H, 2; R = Me, 3). The reaction of complex 1 with 1,2,4-triazole results in the formation of the bistriazolato complex [(mu (5)-C5Me5)(2)Ir-2(mu (2)-H)(mu (2)-eta (1),eta (1)-N3C2H2)(2)](+) (4). Successive protonation of the triazolato ligands in 4 leads to the complexes [(eta (5)-C5Me5)(2)Ir-2(mu (2)-H)(mu (2)-eta (1),eta (1)-N3C2H2)(mu (2)-eta (1),eta (1)-N3C2H3)](2+) (5) and [(eta (5)-C5Me5)(2)Ir-2(mu (2)-H)(mu (2)-eta (1),eta (1)-H3C2H3)(2)](3+) (6). The reaction of 1 with 1,2,3-triazole gives a 1:1 mixture of the bistriazolato complexes [(eta (5)-C5Me5)(2)Ir-2(mu (2)-H)(mu (2)-eta (1),eta (1)-N3C2H2)(2)](+) with parallel (7a) and antiparallel (7b) coordination of the triazolato ligands. The X-ray structure analysis of 3 reveals a diiridium backbone which is bridged by two pyrazolato ligands, the N-N axis being coordinated in a mu (2)-eta (1),eta (1) fashion. (C) 2001 Elsevier Science B.V. All rights reserved.
The cluster dication [(eta(6)-C6H6)(2)(eta(6)-C6Me6)(4)Ru-8(mu(2)-H)(2)(mu(3)-O)(2)(mu(2)-Cl) (2)](2+): a chloro-bridged framework containing two metal tetrahedra
The title complex was obtained by reacting [(eta(6)-C6H6)(eta(6)-C6Me6)(2)Ru-3(mu(2)-H)(3)(mu(3)-O)(+) with RuCl3 . nH(2)O in aqueous solution. it crystallises as the tetrafluoroborate salt. The cationic cluster is formed of two tetrahedral Ru-4 substructures which are held together by two chloro bridges. (C) 2002 Elsevier Science B.V. All rights reserved.
Catalytic hydrogenation of aromatics under biphasic conditions: isolation and structural characterisation of the cluster intermediate [(η6-C6Me6)2(η6-C6H6)Ru3(μ2-H)2(μ2-OH)(μ3-O)]+
The water-soluble cluster cation [(η6-C6Me6)2(η6-C6H6)Ru3(μ2-H)3(μ3-O)]+ (2) catalyses the hydrogenation of benzene and benzene derivatives to give the corresponding cyclohexanes under biphasic conditions. The catalytic activity of 2 depends markedly on the substrate, an extremely high activity being observed for ethylbenzene. The cationic species present in the catalytic mixture of the ethylbenzene hydrogenation could be isolated as the tetrafluoroborate salt and characterised as the cation [(η6-C6Me6)2(η6-C6H6)Ru3(μ2-H)2(μ2-OH)(μ3-O)]+ (3). With 3 as the catalyst, the catalytic activity is also much higher for other benzene derivatives.
Cluster build-up in aqueous solution: synthesis, structure, protonation and catalytic properties of the trinuclear cation [(η6-C6H6)(η6-C6Me6)2Ru3(μ2-H)3(μ3-O)]+
The trinuclear oxo-capped cluster cation [(η6-C6H6)(η6-C6Me6)2Ru3 (μ2-H)3(μ3-O)]+ (2) was synthesised by reacting [(η6-C6Me6)Ru(H2O)3]2+ with [(η6-C6Me6)2Ru2(μ2-H)3]+ in aqueous solution. The single-crystal X-ray structure analysis of the tetrafluoroborate salt shows the cation to contain a H2O molecule hydrogen-bonded to the μ3-oxo ligand. Acidification experiments show two protonation steps occuring at this H2O molecule and the oxo cap of the triruthenium cluster. The cluster cation 2 catalyses the hydrogenation of aromatic compounds in aqueous solution under biphasic conditions.