Ruthenium carbide containing

Figure 33 Reaction scheme for the generation of a ruthenium species containing a terminal carbide.

Polymeric carbon refers to chains of carbon monomers (surface carbide) that are connected by covalent bonds. It has been shown recently47 that the barrier for C-C coupling on flat surfaces (1.22 eV) is half that for a step site (2.43 eV), and may indicate that the growth of these polymeric species is favored on terraces. Polymeric carbon may also refer to carbon chains that contain hydrogen. In the case of CO hydrogenation on ruthenium catalysts, polymeric carbon has been identified as a less reactive carbon that forms from polymerization of CHX and has an alkyl group structure.48... 

The carbide atom in 1 is located in the center of the square face such that it is partially exposed whereas the carbide atom in 2 is completely encapsulated by the six ruthenium atoms. From a spectroscopic viewpoint, carbide atoms are very distinctive and the earlier reviews have dealt with these aspects in detail.7 8 The IR spectrum of 1 contains peaks at 701 (s) and 670(m) cm 1, and 2 contains peaks at 717(sh), 703(s), 680(m), and 669(m) cm-1.22 I3C-NMR spectra of 1 and 2 do not appear to have been reported. This is probably due to the low yields in which these compounds were initially obtained at a time when, 3C-NMR was still not in widespread use in cluster chemistry. In general, the 13C-NMR resonance of carbide atoms ranges from 8 250 to 500. The high frequency resonances exhibited in 13C-NMR spectra reflect the different diamagnetic and paramagnetic effects experienced by a nucleus in such an unusual chemical environment.23... 

Carbides.—That a carbide may be produced during the reduction of chromic oxide by carbon, especially if excess of the latter be used, was first suspected by Deville. In the reduction of an oxide of ruthenium containing oxide of chromium in a carbon crucible, beautiful glittering crystals were obtained. ... 

As mentioned in the Introduction, we can distinguish simple FT catalysts, producing hydrocarbons exclusively with ruthenium as the outstanding example, and complex FT catalysts, such as promoted iron, wherein the steady-state metallic, oxidic, and carbidic phases can coexist. With the latter catalysts the product is a cocktail containing various oxygenates, in particular primary alcohols, as well as hydrocarbons. 

In contrast to [Fe4H2(CO)i3], the analogous hydrides of ruthenium or osmium are stable. Besides tri- and tetranuclear clusters, also known are clusters containing five or six iron or ruthenium atoms and from five to eight osmium atoms as well as carbonyl carbide clusters in which metal atoms are bonded to the carbon atom (Figure 2.22) [Fe5(CO)i5C], [Fcs CO),CV-, [Ru5(CO)i5C],... 

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