Oxidation ruthenium carbonyl clusters

The coordinatively unsaturated cluster [H20s3(CO),o] is found to be cat-alytically active for hydrogenation of alkynes or isomerization of alkenes in solution. Hydridotriosmium and -ruthenium carbonyl clusters bound to a variety of oxides are summarized in Table VIII. The relative activities for... 

Retaining the theme of metal carbonyl clusters, capping considerations in transition-metal clusters have been discussed with reference to [Sb2Co4(CX))] g( A-CX))], and [Bi2Co4(CO)jQ( i-CO)]" 28. An infrared spectroscopic study of the formation of carbonyl rhodium clusters on a rhodium electrode produced by oxidation reduction cycles in acidic solution 2 has also been published. Electrochemistry with ruthenium carbonyls >21 osmium carbonyls 2 jg also reported. Muon spin rotation in a metal-cluster carbonyl compound has been communicated and, lastly, a proton spin-lattice NMR relaxation study of hydride carbonyl clusters has been reported. This provides a method for determining distances involving hydrido ligands... 

Oxidation of metal clusters may also be performed by reaction with Bronsted-acids through straightforward addition of protons to metal backbone. Thus, carbonyl clusters of ruthenium, osmium and iridium are stable in acids and may be pro toned without decomposition. The H-NMR spectra of these carbonyls in concentrated sulfuric or trifluoroacetic acid indicate the formation of cationic metal hydrides ... 

Syntheses of medium- and high-nuclearity ruthenium and osmium clusters continue to be largely by thermolyses of lower nuclearity precursors, but surface-mediated methods have also been employed the use of inorganic oxides or zeolites in the preparation of metal carbonyl clusters, including pentaosmium and hexaruthenium carbido clusters, and the decaosmium complexes [H50sio(CO)24] and [Osio(/t6-C)(CO)24], has been reviewed. 

The early chemistry of hexanuclear carbonyl clusters, including those of ruthenium and osmium, has been reviewed.The hexaruthenium dianion [RuslCOlis] is prepared inside NaX-zeolite cages in 80-90% yields by treatment of [Ru(NH3)6] /NaX with CO and H2. Oxidation of the supported dianion results in cluster degradation to mononuclear ruthenium products, a process that is reversible on re-exposure to CO/H2. A redetermination of the crystal structure of Os6(CO)i8, as its chloroform solvate, confirms the bicapped tetrahedral metal core seen with the unsolvated cluster. 

Indeed, there is a unity with the field of heterogeneous catalysis. As evidence of this, similar (or identical) Rh (C0)2 sites can be prepared either by CO chemisorption on preformed metal particles [69] or by decomposition of rhodium carbonyl clusters on the oxide surface [62-66]. Further evidence for this can be seen from the observation of metal carbonyl clusters under operating supported metal catalysts. For example, ruthenium catalysts for the conversion of synthesis gas to polymethylene [122] afford mixtures of cluster species at elevated temperatures (120°C) and pressures (1000 atm) [123]. One of these was Ru3(CO)i2 others appear to be ill-characterised. A similar observation has been recently reported for Ru/MgO and Os/MgO synthesis gas conversion catalysts [124]. On this basic support, two anionic clusters were isolated, viz. [Ru5C(C0)i5] and [OsiQC(CO)24] 7 which may be synthesised in solution by thermolysis in basic or reducing media. It is unclear whether these clusters are actually effecting the catalysis. They may instead, as highly stable species, be formed in a side reaction. 

Many carbonyl and carbonyl metallate complexes of the second and third row, in low oxidation states, are basic in nature and, for this reason, adequate intermediates for the formation of metal— metal bonds of a donor-acceptor nature. Furthermore, the structural similarity and isolobal relationship between the proton and group 11 cations has lead to the synthesis of a high number of cluster complexes with silver—metal bonds.1534"1535 Thus, silver(I) binds to ruthenium,15 1556 osmium,1557-1560 rhodium,1561,1562 iron,1563-1572 cobalt,1573 chromium, molybdenum, or tungsten,1574-1576 rhe-nium, niobium or tantalum, or nickel. Some examples are shown in Figure 17. 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

We have already alluded to the diversity of oxidation states, the dominance of oxo chemistry and the cluster carbonyls. Brief mention should be made too of the tendency of osmium (shared also by ruthenium and, to some extent, rhodium and iridium) to form polymeric species, often with oxo, nitrido or carboxylato bridges. Although it does have some activity in homogeneous catalysis (e.g. of m-hydroxylation, hydroxyamination or animation of alkenes, see p. 558, and occasionally for isomerization or hydrogenation of alkenes, see p. 571), osmium complexes are perhaps too substitution-inert for homogeneous catalysis to become a major feature of the chemistry of the element. The spectroscopic properties of some of the substituted heterocyclic nitrogen-donor complexes may yet make osmium an important element for photodissociation energy research. 

The recently reported carbide clusters of ruthenium, Rue(CO)i7C and Ru6(CO)i4(arene)C (211), provided a good example of the power of mass spectrometry as an analytical tool. The appearance of the ions Rug(CO) C+ (n = 0-17) provided a clear differentiation between Rue(CO)i7C and another proposed formula Rug(CO)i8 (324). The first carbonyl oxide cluster 0s3(C0)i2 0s04 was characterized by its mass spectrum. The ions 0s404(C0),i+ (n = 0-12) occur in high abundance and the tetranu clear cluster does not rupture until all CO groups are lost (219,220). Other clusters which have been characterized by mass spectrometry include Os3(CO)io(OMe)2 (217), Ru3(CO)i2Xg (X = Cl, Br, I) (212),... 

Ruthenium chemistry typically finds aryloxide ligands attached to the metal in low oxidation states. The extensive number of carbonyl aryloxide compounds reported for this metal exemplifies this (Table 6.34). The cluster compound [(H)2Ru6(CO)i6(M2-0-f -C6H4)] and derivatives contain the metallated phenoxide bridging two metal centres as well as -bound to another. 

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