The question is addressed of whether the triruthenium cluster cation [Ru 3 (µ 2 -H) 3 (η 6 -C 6 H 6 )(η 6 -C 6 Me 6 ) 2 (µ 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 literatures 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 eliminationsthen 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 Neucha ˆtel 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, 4891). 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.

Two saturated N-heterocyclic carbene ligands with substituted naphthyl side chains were used for the preparation of Blechert-type ruthenium metathesis precatalysts. The resulting conformers of the complexes were separated and unambiguously assigned by X-ray diffraction studies. All new complexes were compared in terms of activity to the original, SIMes-derived Blechert catalyst and were shown to be superior. A study on the impact of solvent concentration in RCM reactions using the most active of these new catalysts ultimately led to the ring closing of a variety of substrates at very low catalyst loadings.

A series of second-generation ruthenium-based olefin metathesis catalysts bearing N-naphthylsubstituted N-heterocyclic carbene (NHC) ligands have been prepared and fully characterized. By reaction with the appropriate NHC, these complexes are readily accessible in one synthesis step from the commercially available first-generation precursors [RuCl 2 (dCHPh)(PCy 3 ) 2 ] (Grubbs I, GI) or [RuCl 2 (dCH-o-iPrO-Ph)(PCy 3 )] (Hoveyda-Grubbs I, HGI) by simple exchange of one phosphine ligand with the free NHCs. Time-dependent conversions in the ring-closing metathesis (RCM) of standard substrates leading to di-as well as trisubstituted olefins have been measured for these catalysts. When benchmarked against the parent SIMes-containing the Grubbs II precatalyst (GII), most of these new NHC structures show enhanced reactivity in RCM. From these comparative studies, valuable information was gathered which shows that the alkyl substitution on the naphthyl side chains can enhance or lower the catalytic performance, depending on the bulk and the position of these alkyl groups. The behavior of the best performing precatalysts has been investigated in the RCM of a series of representative substrates, in enyne metathesis reactions as well as in cross-metathesis (CM).

International audienceThe in vitro activity of a series of ruthenium clusters, [(C6H6)(C6Me6)2 Ru3(H)3(O)][BF4], [(C6H6)(1,4-iPrC6H4Me)(C6Me6)Ru3(H)3( O)][BF4], [(C6H6)4Ru4(H)4][BF4]2, [(C6H5Me)4Ru4(H)4][BF4]2 and [(C6H6)4Ru4(H)3(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 [(C6H5Me)4Ru4 (H)4][PF6]2 is also reported