Supported complexes ruthenium carbonyls

Fig. 3.10. Calculated and experimental (FD-MS, cf. Chap. 8.5.4) isotopic pattern of a ruthenium carbonyl porphyrin complex. The isotopic pattern supports the presumed molecular composition. The label is attached to the peak corresponding to the ° Ru-contaming ion. Adapted fromRef. [17] with permission. IM Publications, 1997.

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. 

Although ruthenium is significantly less expensive than rhodium and although its use has been recommended since 1960 (7) for the oxo synthesis, complexes of this metal have not been developed as catalysts. However, many papers and patents have referred to the results obtained employing various ruthenium complexes. The purpose of this article is to analyze the work done involving ruthenium compounds, restricting the scope only to the hydroformylation reaction and not to the carbonylation reaction, which would demand to too lengthy an article. In this review we examine successively mononuclear ruthenium complexes, ruthenium clusters as precursors, photochemical activation, and supported catalysis. 

Immobilization of homogeneous WGS catalysts was reported by Doi ct al. [41] for ruthenium carbonyl complexes modified with phosphine ligands as linkers to silica support material, resulting in a low activity of 0.5 h . RuClj-hydrate immobilized on silica was investigated by means of FT-IR. Upon recrystallization, the formation of dimeric [Ru(CO)3Cl2]2 and [Ru2(CO)i Cl4(H20)] was seen on the surface. Silica was also used to immobilize RuClj [42]. 

Hexaruthenium carbonyl complexes have been used to prepare Ti02-supported mthenium catalysts for the sulfur dioxide reduction with hydrogen [112, 113], A catalyst derived from [Ru6C(CO)i6] showed higher activity in the production of elemental sulfur at low temperatures than that prepared from RUCI3 as precursor. This catalytic behavior is related with the formation of an amorphous ruthenium sulfide phase that takes place during the reaction over the ex-carbonyl catalyst [112]. 

Ruthenium catalysts prepared from Ru3(CO)i2 and other related carbonyl-derived complexes have been widely used in reactions of hydrogenolysis, homologation and dimerization of alkanes [114—116]. Catalysts derived from carbonyl precursors usually show higher catalytic activities than conventionally prepared supported mthenium catalysts. This correlates well with the smaller crystallite size achieved by using carbonyl precursors. 

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