Photochemical Activation and Supported Catalysis

Many efforts have been undertaken to graft transition metal complexes onto various supports in order to retain the performance of the soluble catalyst precursors and to allow easy separation of the catalysts from the reaction products. Most studies have been concerned with polymers, particularly with functionalized styrene-divinylbenzene resins. This approach to immobilize homogeneous catalysts has been reviewed, with all the strategies to anchor metal complexes on organic or inorganic supports examined (57-59). 

When the equilibrium is shifted to right the hydrido ligands present a more hydridic character, so that more linear alkyl species are formed. 

A similar approach has been carried out by Kim et al. (62) who disclosed the use of sulfbnated styrene-divinylbenzene resins plus a tris(dialkyla-minophosphine) to obtain a phosphonium attached salt which can exchange triphenylphosphine ligands in [Ru(CO)3(PPh3)2] or [RUCI2- 

The use of metal phthalocyanine compounds has also been described (66,67). The catalysts can either be supported on an inert carrier or used in a liquid-liquid two-phase system. Various functionalized phthalocyanine ruthenium complexes have been mentioned for the reaction of interest. For instance, ruthenium phthalocyanine disulfonate transformed hept-3-ene into 3- -propylpentanol (80°C, 18 hours, 120 bar) in a two-phase system. Further details (67) on the preparation of metal complexes supported on silica- and alumina-type supports have appeared. Generally, a mixture of metal phthalocyanine sulfonate and hydrated alumina pro- 

Transition metal carbonyl clusters intercalated with lamellar materials such as graphite or smectites have been prepared and have been shown to be useful in catalysis 68). For instance, sodium montmorillonite was impregnated with [Ru(NH3)5]Cl3 in water under reflux. After flltration and drying, the resulting complex was dissolved in methanol and reduced with carbon monoxide at 80°C, 100 bar, for 16 hours. Infrared analysis has shown the formation of a sodium montmorillonite-intercalated [Ru3(CO),2] complex. This system was claimed to be active for the hydro-formylation of propene either with CO/Hj or CO/HjO in the presence of a basic promoter. 

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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. 

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