Rhodium triphos catalyst

Scheme 8.5 Synthesis of a rhodium triphos catalyst and the mechanism of the catalytic...

Removal of sulfur from these complexes remains challenging. Catalysts such as [M(COD)(PPh3)2]+ (M = Rh, Ir) only hydrogenate the C=C bond of benzothio-phene, whereas the hydrogenation with rhodium triphos complexes gives 2-ethyl-thiophenol.148 The addition of Co4(CO)i2 to (21-XXVIII, ML, = Cp Ir), however, leads to partial desulfurization, presumably with formation of cobalt sulfide.149... 

Wagner, B, Heneghan, M, Schnabel, G, Ernst, B, Catal)4ic glycosylation with rhodium(III)-triphos catalysts, Synlett, 1303-1306, 2003. 

An example of a noncovalent attachment of a metal-phosphine complex to a solid support is presented in Figure 31, as reported by Bianchini et al. (120). The complex is attached via a sulfonated variant of the "triphos" ligand, which is known for its successful application in several catalytic reactions. The ligand is attached to the silica by an ionic bond, which is stable in the absence of water. The catalyst was used for the hydroformylation of styrene and of hex-1-ene in batch mode and showed moderate activity. The triply coordinated rhodium atom is strongly boimd although the conditions were rather harsh (120 °C, 30 bar) the concentration of leached metal measured by atomic emission spectroscopy was at most at the parts per million level. However, for commercial applications, for example, in a process such as hydroformylation of bulk products, these concentrations should be less than 10 ppb 111,121). 

While metal complexes capable of desulfurizing or hydrodesulfurizing thiophenes are relatively numerous, homogeneous catalysts are very rare, being limited to rhodium and iridium TRIPHOS precursors that are unique in tolerating the harsh experimental conditions required for the second C-S bond cleavage of thiophenes [2 b]. 

More recent work on the hydrogenation of thiophenic molecules catalyzed by water-soluble metal complexes is pursuing the use of polyphosphine ligands (cf. Section 3.2.2). These studies follow the success obtained with the tridentate phosphine MeC (CH2PPh2)3 (TRIPHOS), which forms rhodium and iridium catalysts for the hydrogenation, hydrogenolysis, and desulfurization of various thiophenic... 

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