Improving Grubbs’ II type ruthenium catalysts by appropriately modifying the N-heterocyclic carbene ligand

The introduction of N-heterocyclic carbene ligands that incorporate correctly substituted naphthyl side chains leads to increased activity and stability in second generation ruthenium metathesis catalysts

[η6-2-(2-Methylbenzoyloxy)ethyl methacrylate]bis(η6-1,2,4,5-tetramethylbenzene)tri-μ-hydrido-μ3-oxo-triruthenium(II)(3Ru—Ru) tetrafluoroborate

The trinuclear arene-ruthenium cluster cation, [Ru3H3(O)(C10H14)2(C14H16O4)](+), has been synthesized and crystallized as the tetrafluoroborate (BF4-) salt. The cations form, along the b axis, infinite one-dimensional chains through pi-stacking interactions

Supramolecular triruthenium cluster-based benzene hydrogenation catalysis: Fact or fiction?

The question is addressed of whether the triruthenium cluster cation [Ru-3(mu(2)-H)(3)(eta(6)C(6)H(6))(eta(6)-C6Me6)(2)(mu(3)-O)](+), 1, is a supramolecular, outer-sphere benzene hydrogenation catalyst or is 1 a precatalyst to well-known Ru(0)(n) catalysis of benzene hydrogenation. This question of "is it homogeneous or heterogeneous catalysis?" is especially important in the present case since if 1 is a supramolecular, homogeneous catalyst as postulated in the literature that is, if 1 can in fact accomplish catalysis of reactions as difficult as benzene reduction with no inner-sphere, d-orbital-mediated ligand dissociation, oxidative addition, migratory insertion, or reductive elimination-then that finding holds promise of rewriting the rules of organometallic-based catalysis. The identity of the true catalyst derived from 1 is, therefore, addressed by a collaborative effort between research groups at the Universite de Neuchatel and Colorado State University. The methodology employed is that worked out previously for addressing the historically vexing question of "is it homogeneous or heterogeneous catalysis?" (Lin, Y.; Finke, R. G. Inorg. Chem. 1994, 33, 489 1). A combination of the following classes of experiments have been employed: (i) Ru metal product studies; (ii) kinetic studies; (iii) Hg(0) and quantitative poisoning experiments, (iv) NMR studies of H/D exchange rates; (v) other data, plus (vi) the principle that the correct mechanism will explain all of the data. The results provide a compelling case that 1 is not the true benzene hydrogenation catalyst as previously believed; instead, all our evidence is consistent with, and supportive of, trace Ru(0) derived from 1 under the reaction conditions as the true, active catalyst. Nine additional conclusions are also presented as part of the summary and take-home messages, as well as a citation of "Halpern's rules" for catalysis

Supramolecular triruthenium cluster-based benzene hydrogenation catalysis: Fact or fiction?

The question is addressed of whether the triruthenium cluster cation [Ru-3(mu(2)-H)(3)(eta(6)C(6)H(6))(eta(6)-C6Me6)(2)(mu(3)-O)](+), 1, is a supramolecular, outer-sphere benzene hydrogenation catalyst or is 1 a precatalyst to well-known Ru(0)(n) catalysis of benzene hydrogenation. This question of "is it homogeneous or heterogeneous catalysis?" is especially important in the present case since if 1 is a supramolecular, homogeneous catalyst as postulated in the literature that is, if 1 can in fact accomplish catalysis of reactions as difficult as benzene reduction with no inner-sphere, d-orbital-mediated ligand dissociation, oxidative addition, migratory insertion, or reductive elimination-then that finding holds promise of rewriting the rules of organometallic-based catalysis. The identity of the true catalyst derived from 1 is, therefore, addressed by a collaborative effort between research groups at the Universite de Neuchatel and Colorado State University. The methodology employed is that worked out previously for addressing the historically vexing question of "is it homogeneous or heterogeneous catalysis?" (Lin, Y.; Finke, R. G. Inorg. Chem. 1994, 33, 489 1). A combination of the following classes of experiments have been employed: (i) Ru metal product studies; (ii) kinetic studies; (iii) Hg(0) and quantitative poisoning experiments, (iv) NMR studies of H/D exchange rates; (v) other data, plus (vi) the principle that the correct mechanism will explain all of the data. The results provide a compelling case that 1 is not the true benzene hydrogenation catalyst as previously believed; instead, all our evidence is consistent with, and supportive of, trace Ru(0) derived from 1 under the reaction conditions as the true, active catalyst. Nine additional conclusions are also presented as part of the summary and take-home messages, as well as a citation of "Halpern's rules" for catalysis

Remarkable anticancer activity of triruthenium-arene clusters compared to tetraruthenium-arene clusters

The in vitro activity of a series of ruthenium clusters, [(eta(6)-C6H6)(eta(6)-C6Me6)(2)Ru-3(mu-H)(3)(mu(3)-O)][BF4], [(eta(6)-C6H6)(eta(6)-1,4-(PrC6H4Me)-Pr-i)(eta(6)-C6Me6)Ru-3(mu-H)(3)(mu (3)-O)][BF4], [(eta(6)-C6H6)(4)Ru-4(mu-H)(4)][BF4](2), [(eta(6)-C6H5Me)(4)Ru-4(mu-H)(4)][BF4](2) and [(eta(6)-C6H6)(4)Ru-4(mu-H)(3)(mu-OH)][Cl](2), has been evaluated against A2780 and A2780cisR ovarian carcinoma cell lines. Both triruthenium clusters are very active compared to ruthenium compounds in general, whereas the tetraruthenium clusters do not display significant cytotoxicities. Since the triruthenium clusters are known to form supramolecular interactions with arenes and other functions, it is possible that such interactions are also important with respect to their mode of biological activity. The X-ray structure analysis of [(eta(6)-C6H5Me)(4)Ru-4(mu-H)(4)][PF6](2) is also reporte

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 ail aqueous solution of 1 to air yields the oxidised cluster [H2RU3(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 I and 2 in the same medium affords only decomposition products. Ligand exchange in I takes place only at higher temperatures: by heating a mixture of toluene with ail aqueous solution of [1][BF4] (1000: 1) to 110 degrees 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 degrees C however, in the presence of D-2, H/D exchange with 1 is observed to give the deuterated derivative [D3RU3(C6H6)(C6Me6)(2)(O)](+) (1a). The results provide ail 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

Synthesis and Characterization of Tetrahedral Ru3O Clusters with Intrinsic Framework Chirality: A Chiral Probe of the Intact Cluster Catalysis Concept

To bring evidence for or against the hypothesis of catalytic hydrogenation by intact trinuclear arene ruthenium clusters containing an oxo cap, cationic Ru3O clusters with three different arene ligands (intrinsically chiral tetrahedra) have been synthesized as racemic mixtures. By introduction of a chiral auxiliary substituent at one of the three different arene ligands, the separation of the two diastereomers was possible. The chiral Ru3O framework was evidenced by X-ray crystallography, by circular dichroism in the UV and IR regions, and by chiral shift reagents in the NMR spectra. The catalytic hydrogenation of the prochiral substrate methyl 2-acetamidoacrylate using a chiral Ru3O cluster showed no asymmetric induction, suggesting that the catalytically active species is not the intact Ru3O cluster