Rhodium catalysts containing sulfonated

Itsimo [25] has also shown that polymer-supported OPEN monosulfonamides containing sulfonated pendent group (Scheme 16) are able to catalyze the HTR reduction of ketones in water with sodium formiate as hydrogen donor (S/C = 100). However, TsDPEN immobilized on polystyrene crosslinked or not, polymer 30 and 31 respectively, shrank in water. Sodium /j-styrene sulfonate was copolymerized with chiral A-(vinylbenzene-p-sulfonyl)-DPEN (20) imder radical polymerization conditions with or without DVB leading respectively to ligand 32 and 33. Control of the balance hydrophilicity/hydrophobieity of the polymer support is carried out by changing the salt from Na to quaternary ammonium. All of these polymers swelled in water, and their respective ruthenium, rhodium or iridium complexes were prepared. Compared to sodium salt polymer-supported catalyst from 32a and 33a, ammonium... 

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... 

Rhin(bpy)3]3+ and its derivatives are able to reduce selectively NAD+ to 1,4-NADH in aqueous buffer.48-50 It is likely that a rhodium-hydride intermediate, e.g., [Rhni(bpy)2(H20)(H)]2+, acts as a hydride transfer agent in this catalytic process. This system has been coupled internally to the enzymatic reduction of carbonyl compounds using an alcohol dehydrogenase (HLADH) as an NADH-dependent enzyme (Scheme 4). The [Rhin(bpy)3]3+ derivative containing 2,2 -bipyridine-5-sulfonic acid as ligand gave the best results in terms of turnover number (46 turnovers for the metal catalyst, 101 for the cofactor), but was handicapped by slow reaction kinetics, with a maximum of five turnovers per day.50... 

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. 

Homogeneous catalysis by transition metal complexes almost always involves processes in which product-catalyst separation and catalyst recycling are important issues. For years, researchers have worked to find effective ways to isolate metal-complex catalysts in phases separate from those containing the catalyst, usually by anchoring the metal complex to a solid surface. As summarized by Driessen-Holscher, it is now evident that the method that has met with most practical success in this direction involves the use of multiple liquid phases. For example, rhodium complexes with water-soluble sulfonated ligands are used to catalyze alkene hydroformyla-tion, and the aqueous-phase catalyst and the organic products are easily separated as insoluble liquid phases. 

In continuous operation phosphoms-containing consecutive products are formed which also influence the activity of the rhodium center and thus contribute to the catalyst deactivation. One of the main degradation products from TPPTS is the sodium salt of m-formylbenzene sulfonic acid, which indicates the insertion of the rhodium atom into the P-C bond. 

The functional group tolerance of this reaction is illustrated by olefins containing ester, amide, sulfone, and nitrile groups which can be applied to RhCl(PPh3)3-catalyzed orthoalkylation with remarkable efficiency (eq 68). These functionalized olefins are much more reactive than nonfunctionaUzed olefins. Nevertheless, when rhodium cationic species are employed as a catalyst, much higher yields of orthoalkylated products can be obtained under mild reaction conditions. 

Henbest and Trocha-Grimshaw have shown that sulfoxides may be oxidized to sulfones in the presence of iridium and rhodium complexes [139, 140]. Oxidations were studied by passing air through a solution of the sulfoxide in hot wopropanol containing 10% water in the presence of the catalyst. Sulfones were formed when chlorides of iridium or rhodium were used while chlorides of ruthenium, osmium and palladium were not effective. Under reaction conditions the chlorides should be converted wholly or partly to metal sulfoxide complexes. 

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