Ruthenium complexes hydride clusters

Osmium-Carbonyl-Hydride Clusters and Related Ruthenium Complexes. Our investigation of these species began with a study of the species (/i2-H)(H)Os3(CO)n, prepared from Os3(CO)i2 via the unsaturated species (M2-H)20s3(CO)io (33) (see Reaction 1). 

The reactions of tin hydrides with metal-metal bonded clusters has proven to be a successful route to a range of metal-tin bonded complexes. Products usually result in the cleavage of the M—M bond however, under special conditions, for example with bridging ligands, the bond can remain intact and result in either bridging or terminal tin groups, as shown for some ruthenium and osmium clusters (equations 102 and 103). 

Rhodium-based catalysis suffers from the high cost of the metal and quite often from a lack of stereoselectivity. This justifies the search for alternative catalysts. In this context, ruthenium-based catalysts look rather attractive nowadays, although still poorly documented. Recently, diruthenium(II,II) tetracarboxylates [42], polymeric and dimeric diruthenium(I,I) dicarboxylates [43], ruthenacarbor-ane clusters [44], and hydride and silyl ruthenium complexes [45 a] and Ru porphyrins [45 b] have been introduced as efficient cyclopropanation catalysts, superior to the Ru(II,III) complex Ru2(OAc)4Cl investigated earlier [7]. In terms of efficiency, electrophilicity, regio- and (partly) stereoselectivity, the most efficient ruthenium-based catalysts compare rather well with the rhodium(II) carboxylates. The ruthenium systems tested so far seem to display a slightly lower level of activity but are somewhat more discriminating in competitive reactions, which apparently could be due to the formation of less electrophilic carbenoid species. This point is probably related to the observation that some ruthenium complexes competitively catalyze both olefin cyclopropanation and olefin metathesis [46], which is at variance with what is observed with the rhodium catalysts. 

On comparing H NMR spectra obtained for the reaction of para-H2 with X at different reaction times (fig. 10), it can be seen that the H2 signal starts as an enhanced negative value (due to the initial transfer from para-H2), and then reaches its thermal equilibrium value by a complex mechanism basically determined by the relaxation rates of the protons in the ruthenium complex. Clearly, the exchange rate of H2 over the triruthenium cluster should be faster than the relaxation rate of the hydride ligands, otherwise no memory of the intermediate state could have been revealed in the molecular hydrogen resonance. [56]... 

The synthetic methods used involve reaction of a cluster anion with [AuCIL], elimination of methane between a cluster hydride and [AuMeL] or addition of LAu+ units to metal-metal bonds. The emphasis here will be on structure and reactions of the complexes. Some examples of mixed gold clusters are given in Table 15, where it can be seen that most work has been on derivatives of clusters of iron, ruthenium and osmium. 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

The clusters (18), (19), (20), and [H2Rn8(CO)2i] (21) are all products from reacting Ru3(CO)i2 nnder different conditions. (18), the major product in the synthesis of all of these complexes, has an octahedral core of ruthenium atoms, with an interstitial hydride. The hydride seems to have some stabilizing effect on the octahedral complex, since all products of higher nuclearity are based on this octahedral framework. As seen in Scheme 6, the structure of the octaruthenium dihydride complex (21) resembles an octahedron with an additional Ru2 unit. Another Ru2 unit is added to this complex... 

However, only alkyl formates are formed in the conventional reactions of alcohols, CO2 and H2 using transition metal complexes, because intermediary hydride complexes generally react with CO2 to give formate complexes. On the other hand, we have found that mthenium cluster anions effectively catalyze the hydrogenation of CO2 to CO, methanol, and methane without forming formate derivatives [2-4]. Ethanol was also directly formed from CO2 and H2 with ruthenium-cobalt bimetallic catalyst [5]. In this paper, we report that this bimetallic catalytic... 

Some analogous ruthenium- and osmium-bismuth clusters have been found. Examples include Bi2M3(CO)g and H3BiM3(CO)g (M = Ru, Os). The structures of the hydride compounds have both been determined and they are isostructural with the iron complexes as is Bi2Ru3(CO)g with Bi2Fe3(CO)g. The structure of Bi20s3(C0)g, on the other hand, has not been determined and its IR spectrum indicates that it probably has a different structure. A spirocyclic cluster [Ru2(CO)8Gu.4-Bi)Ru3(CO)io(/u.-H)] (39) has been reported. 

Exclusive of metal-metal bonding, the six metal atoms in the octahedral cluster metal carbonyls Mg(CO)10 (M = Co, Rh, and Ir) as well as their iso-electronic analogs Me(CO)i52 and Mg (CO) have (6)(9) + (2)(16) = 86 outer valence electrons. The hydride H2Rug(CO)i0 and the carbide Rug(C0)i7C are two types of octahedral cluster ruthenium carbonyl complexes that likewise have 86 outer valence electrons exclusive of metal-metal bonding and thus may be regarded as isoelectronic with Mg(CO) g (M = Co, Rh, and Ir). 

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