Ruthenium cluster catalysts

The Elsevier system has since been shown to carry out several ester hydrogenations that were previously deemed impossible [114]. The hydrogenation of dimethyl phfhalate to phfhalide with ruthenium cluster catalysts has already been discussed (Table 15.15, Entry 4). The application of [Ru(acac)3] and triphos -this time with a 20-fold excess of Et3N as additive - delivers good yields of phthalide. However, the use of isopropanol (I PA) as solvent and 24% HBF4 allows further hydrogenation to 1,2,-bis-hydroxylmethyl benzene for the first time. Both of these reactions were carried out under milder conditions (100°C, 85 bar H2, 16 h) than those reported previously. 

In addition to hydroformylation, metal catalysed hydrogenation processes have been studied at length including hydrogenation of a-olefins, aromatics and asymmetric hydrogenations of more complex substrates. Benzene can be selectively fully hydrogenated by using a ruthenium cluster catalyst in [Bmim][BF4]. ... 

Dyson, P.J. Ellis, D.J. Parker, D. G. Welton,T., Arene Hydrogenation in a Room-Temperature Ionic Liquid Using a Ruthenium Cluster Catalyst. Chem. Commun. 1999,25. 

The choice of catalyst can have a significant effect on these ratios. For reaction 26.5, a cobalt carbonyl catalyst (e.g. HCo(CO)4) gives a 80% C4-aldehyde, 10% C4-alcohol and 10% other products, and an h ratio 3 1. For the same reaction, various rhodium catalysts with phosphine cocatalysts can give an n i ratio of between 8 1 and 16 1, whereas ruthenium cluster catalysts show a high chemo-selectivity to aldehydes with the regioselectivity depending on the choice of cluster, e.g. for Ru3(CO)i2, a 2 1, and for [HRu3(CO)ii], 74 1. Where the hydroformylation... 

P.J. Dyson, D.J. ElUs, D.G. Parker et al., Arene hydrogenation in a room-temperature ionic liquid using a ruthenium cluster catalyst. Chem. Commun. 1 (1999) 25-26. 

When the ruthenium EXAFS for the ruthenium-copper catalyst is compared with the EXAFS for a ruthenium reference catalyst containing no copper, it is found that they are not very different. This indicates that the environment about a ruthenium atom in the bimetallic catalyst is on the average not very different from that in the reference catalyst. This result is consistent with the view that a ruthenium-copper cluster consists of a central core of ruthenium atoms with the copper atoms present at the surface. 

The copper EXAFS of the ruthenium-copper clusters might be expected to differ substantially from the copper EXAFS of a copper on silica catalyst, since the copper atoms have very different environments. This expectation is indeed borne out by experiment, as shown in Figure 2 by the plots of the function K x(K) vs. K at 100 K for the extended fine structure beyond the copper K edge for the ruthenium-copper catalyst and a copper on silica reference catalyst ( ). The difference is also evident from the Fourier transforms and first coordination shell inverse transforms in the middle and right-hand sections of Figure 2. The inverse transforms were taken over the range of distances 1.7 to 3.1A to isolate the contribution to EXAFS arising from the first coordination shell of metal atoms about a copper absorber atom. This shell consists of copper atoms alone in the copper catalyst and of both copper and ruthenium atoms in the ruthenium-copper catalyst. 

Since ruthenium and rhodium are neighboring elements in the periodic table, a closer comparison of the properties of ruthenium-copper and rhodium-copper clusters is of interest (17). When we compare EXAFS results on rhodium-copper and ruthenium-copper catalysts in which the Cu/Rh and Cu/Ru atomic ratios are both equal to one, we find some differences which can be related to the differences in miscibility of copper with ruthenium and rhodium. The extent of concentration of copper at the surface appears to be lower for the rhodium-copper clusters than for the ruthenium-copper clusters, as evidenced by the fact that rhodium exhibits a greater tendency than ruthenium to be coordinated to copper atoms in such clusters. The rhodium-copper clusters presumably contain some of the copper atoms in the interior of the clusters. 

There has been great interest in the preparation of bimetallic transition metal cluster complexes containing palladium.899-902 Bimetallic palladium-ruthenium clusters have been shown to be good precursors to supported bimetallic catalysts.903,904... 

Ruthenium cluster compounds (143) and (144) have been identified that may play a role in the catalysis when Ru3(CO)12 was used as the precursor.540-543 The use of [(dppe)Ru(CO)3] as a catalyst including the intermediates (145) and (146) in the catalytic cycles, have been studied in detail by Gladfelter and co-workers.544-550... 

More recently, the ruthenium-catalyzed hydrogenation of sorbic acid to cis-hex-3-enoic acid. Scheme 16, was achieved in a biphasic bmim-PF6-methyl tert- miy ether (MTBE) system. The ruthenium cluster [H4Ru(q -C6H6)4] [Bp4]4, in [bmim][BF4], was shown to be an effective catalyst for the hydrogenation of arenes to the corresponding cycloalkanes at 90 °C and 60 bar. The cycloalkane product formed a separate phase, which was decanted and the IL phase, containing the catalyst, could be repeatedly recycled. 

Decomposition of the trimethylsilyl diazoacetate 133 with a ruthenium cluster in the presence of benzaldehyde and dimethylfumarate led to formation of the THE derivative 135 in 54% isolated yields. The ruthenium catalyst proved superior to all standard rhodium complexes for this transformation. 

A complex nanostructured catalyst for ammonia synthesis consists of ruthenium nanoclusters dispersed on a boron nitride support (Ru/BN) with barium added as a promoter (33). It was observed that the introduction of barium promoters results in an increase of the catalytic activity by 2—3 orders of magnitude. The multi-phase catalyst was first investigated by means of conventional HRTEM, but this technique did not succeed in identifying a barium-rich phase (34). It was even difficult to determine how the catalyst could be active, because the ruthenium clusters were encapsulated by layers of the boron nitride support. By HRTEM imaging of the catalyst during exposure to ammonia synthesis conditions, it was found that the... 

The ruthenium cluster [Ru2(i76-C6H6)H6]C12 is a catalyst for fumaric acid hydrogenation in aqueous solutions, with a turnover frequency of 35 h 1 at 50°C (86). 

Recent work by Ford et al. demonstrates that a variety of metal carbonyl clusters are active catalysts for the water-gas shift under the same reaction conditions used with the ruthenium cluster (104a). In particular, the mixed metal compound H2FeRu3(CO)13 forms a catalyst system much more active than would be expected from the activities of the iron or ruthenium systems alone. The source of the synergetic behavior of the iron/ruthenium mixtures is under investigation. The ruthenium and ruthenium/iron systems are also active when piperidine is used as the base, and in solutions made acidic with H2S04 as well. Whether there are strong mechanistic similarities between the acidic and basic systems remains to be determined. 

Synthesis of Methylformate by C02 Reduction with Molecular Hydrogen in the Presence of Methanol Using Ruthenium Clusters as Catalysts... 

Cobaltocenium calix[4]arene receptors, characteristics, 12,475 Cobaltocenium-metallacarborane salts, preparation, 3, 23 Cobaltocenium receptors, characteristics, 12, 474 Cobalt phosphines, as supports, 12, 683 Cobalt-platinum nanoparticles, preparation, 12, 74 Cobalt-ruthenium clusters, as heterogeneous catalyst precursors, 12, 768... 

Shephard, D. S., Maschmeyer, T., Sankar, G., Thomas, J. M., Ozkaya, D., Johnson, B. F. G., Raja, R., Oldroyd, R. D. and Bell, R. G. Preparation, characterization and performance of encapsulated copper-ruthenium bimetallic catalysts derived from molecular cluster carbonyl precursors, Chem. Eur. J., 1998, 4, 1214-1224. 

Carbonylation at a C-H bond fi to the sp2 ring nitrogen can also be achieved by a Ru3(CO)12 catalyst. The Ru3(CO)12-catalyzed reaction of 1,2-dimethyl-benzimidazole with an alkene and CO provides the corresponding /J-acylated product in high yield with complete site-selectivity [42] (Eq. 25). A tri-nuclear ruthenium cluster 19 is proposed as the key catalytic species. A similar basicity-dependent reactivity of substrates as described in the a-carbony-lation was observed in the case of the carbonylation at C-H bond to the sp2 nitrogen. 

It has been also found that the platinum-ruthenium cluster complex [Pt3Ru6(CO)20(p3-PhC2Ph)(p3-H)(p-H)] is an effective catalyst precursor for the highly selective catalytic hydrosilylation of diphenylacetylene with tri-ethoxysilane (Eq. 15). The true catalyst is actually the decarbonylated species. 

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