Ruthenium, high nuclearity carbonyl

Finally, the surface-mediated synthesis of ruthenium carbonyl complexes has also been used to prepare supported ruthenium particles. Using silica as a reaction medium and conventional salts, apart from Ru3(CO)i2, mononuclear Ru(CO)j, and high nuclearity carbonyl-derived species can be obtained by CO reductive carbonylation [127, 128]. This opens new routes to preparing tailored supported ruthenium particles. 

Interest in the high nuclearity carbonyl clusters of ruthenium has centered around the hexanuclear carbido-cluster Ru6C(CO)17 and its derivatives, Ru5C(CO)15 and, more recently, [Ru C CO) ]2-.1 The chemistry of both Ru6C(CO)17 and Ru5C(CO)15 has been investigated in some detail. Their syntheses are described below. 

Ruthenium and, particularly, osmium form a great many high nuclearity carbonyl clusters. Only a few illustrative examples can be mentioned here. Figure 18-F-6 shows some of the topological relationships among the osmium compounds. The scope of the ruthenium chemistry has been extended recently with the preparation of the [RuioH2(CO)25]2 and [RunH(CO)27]3 ions.137... 

Fig. 5.4 depicts some results obtained in the first stages (high nuclearity complexes formation) of the synthesis in xylene solvent which leads to the formation of nanostructured powders, RuxSey, from tris-ruthenium dodeca-carbonyl (Ru3(CO)i2) and elemental selenium dissolved in an organic solvent (xylene). After 40 minutes of reaction, l3C-NMR spectrum (Fig. 5.4 (c)) puts in evidence the formation of a new polynuclear chemical precursor with a chemical shift 8 of 198.89 ppm (i.e., Ru4Se2(CO)n)- Selenium takes part in the coordination sphere. The peak intensity with the chemical shift of 199.67 ppm, corresponds to the initial chemical precursor which decreases as a function of the synthesis reaction time (Fig. 5.4(a)). Other chemical shifts (with minor peak intensities) on both sides of the 13C-NMR spectrum, which put in evidence the complex interplay of the reaction, are also observed. 

M. P. Cifuentes, M. G. Humphrey, J. E. McGrady, P. J. Smith, R. Stranger, K. S. Murray, and B. Moubaraki, High Nuclearity Ruthenium Carbonyl Cluster Chemistry. 5. Local Density Functional, Electronic Spectroscopy, Magnetic Susceptibility, and Electron Paramagnetic Resonance Studies on (Carbido)decaruthenium Carbonil Clusters, J. Am. Chem. Soc. 119,2647-2655 1997. 

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. 

Advances in spectroscopic characterization continue to drive the development of the field. A number of studies describing the mass spectrometry of medium- and high-nuclearity ruthenium and osmium carbonyl clusters have been reported, including UV-laser desorption, laser desorption/ionization time-of-flight and energy-dependent electrospray ionization the last mentioned has been shown to resolve mixtures of cluster compounds. 

The lowest nuclearity carbidocarbonyl clusters of ruthenium and osmium are RujC(CO)1J( 10, andOs5C(CO),s, 11. The former is synthesized in high yield by the carbonylation of Ru6C(CO),7 (see below) under precisely determined conditions of temperature and pressure [Eq. (9)] (29). 

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. 

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