Rhodium catalysts containing sulfonated phosphine

In 1975 Kuntz has described that the complexes formed from various rhodium-containing precursors and the sulfonated phosphines, TPPDS (2) or TPPTS (3) were active catalysts of hydroformylafion of propene and 1-hexene [15,33] in aqueous/organic biphasic systems with virtually complete retention of rhodium in the aqueous phase. The development of this fundamental discovery into a large scale industrial operation, known these days as the Ruhrchemie-Rhone Poulenc (RCH-RP) process for hydroformylation of propene, demanded intensive research efforts [21,28]. Tire final result of these is characterized by the data in Table 4.2 in comparison with cobalt- or rhodium-catalyzed processes taking place in homogeneous organic phases. 

These materials are prepared by the covalent attachment of ionic hquids to the support surface or by simple deposition of the ionic liquid phases containing catalytically active species on the surface of the support (usually silica-based or polymeric materials including membranes). In various cases, the procedure involves the simple dissolution of a sulfonated phosphine-modified rhodium catalyst into a supported ionic liquid, while the alkene constitutes the organic phase. This method reduces the amount of ionic liquid and allows for a facUe and efficient separation of products from catalyst. In comparison to traditional biphasic systems, higher catalytic activity and lower metal leaching can be obtained by appropriately tuning the experimental conditions [35—41]. 

Although rhodium recovery is efficient it is difficult to separate it from heavies that are formed in small amounts. Over time these heavies tend to result in some catalyst deactivation. One solution to this problem has been developed by Ruhrchemie/Rhone-Poulenc. In this process sulfonated triphenyl phosphine is used as the ligand, which imparts water solubility to the catalyst. The reaction is two-phase, a lower aqueous phase containing the catalyst and an upper organic phase. Fortunately the catalyst appears to sit at the interface enabling reaction to proceed efficiently. At the end of... 

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