Rhodium complexes supported catalysis

Polymer-supported catalysts incorporating organometaUic complexes also behave in much the same way as their soluble analogues (28). Extensive research has been done in attempts to develop supported rhodium complex catalysts for olefin hydroformylation and methanol carbonylation, but the effort has not been commercially successful. The difficulty is that the polymer-supported catalysts are not sufftciendy stable the valuable metal is continuously leached into the product stream (28). Consequendy, the soHd catalysts fail to eliminate the problems of corrosion and catalyst recovery and recycle that are characteristic of solution catalysis. 

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. 

SAPC can perform a broad spectrum of reactions such as hydroformylation, hydrogenation and oxidation, for the synthesis of bulk and fine chemicals, pharmaceuticals and their intermediates. Rhodium complexes are the most extensively used, but complexes of ruthenium, platinum, palladium, cobalt, molybdenum and copper have also been employed [63-65]. Owing to interfacial reactions, one of the main advantages of SAPC upon biphasic catalysis is that the solubility of the reactant in the catalytic aqueous-phase does not limit the performance of the supported aqueous phase catalysts. 

The metal complexes most often studied as polymer-bound catalysts have been Rh(I) complexes, such as analogues of Wilkinson s complex. The catalytic activity of a bound metal complex is nearly the same as that of the soluble analogue. Rhodium complexes are active for alkene hydrogenation, alkene hydroformylation, and, in the presence of CH3I cocatalyst, methanol carbonylation, etc. Polymer supports thus allow the chemistry of homogeneous catalysis to take place with the benefits of an insoluble, easily separated catalyst . ... 

Amino-derived BDPP (2,4-bis[diphenylphosphino]pentane) has been used in asymmetric hydrogenation catalysis [15-17] (cf. Sections 6.2 and 6.9). NMR analysis showed that a ten-fold excess of HBF4 is sufficient to protonate reversibly all four amino groups in the [Rh(diene)(BDPP)]BF4 complex. Recycling of the catalyst after enantioselective hydrogenation of dehydroamino acid derivatives in methanol is achieved by acidification with aqueous FIBF4 followed by extraction of the product with Et20. Immobilization of the protonated BDPP rhodium complex on a Nafion support has been studied as well [18]. 

For example, the homogeneous base case with 1-hexene as a substrate showed a fej, of 0.4 min at a reaction temperature of 50 °C, while the supported IL catalyst achieved a fejj of 11.2 min for the same reaction at 30 °C. The enhanced activity of the rhodium complex in an IL phase had been observed previously and may be explained by the absence of any coordinating solvent [17]. In an acetone solution under hydrogen pressure the complex exhibited coordination of two solvent molecules to the metal center. In theory, if the catalysis is carried out in an IL... 

Hughes, O.R. and Unruh, J.D. (1981) Hydroformylation catalyzed by rhodium complexes with diphosphine ligands. Journal of Molecular Catalysis, 12,71 Sanger, A.R. (1977) Hydroformylation of 1-hexene catalysed by complexes of rhodium(I) with di- or tritertiary phosphines. Journal of Molecular Catalysis, 3,221 Sanger, A.R. and Schallig, L.R. (1977) The structures and hydroformylation catalytic activities of polyphosphine complexes of rhodium(l), and related complexes immobilised on polymer supports. Journal of Molecular Catalysis, 3, 101 Pittman, C.U. and Hirao, A. (1978) Hydroformylation catalyzed by cis-chelated rhodium complexes - extension to polymer-anchored cis-chelated rhodium catalysts. The Journal of Organic Chemistry, 43, 640. 

Duml973 Dumont, W., Poulin, J.C., Dang, T.P. and Kagan, H.B., Asymmetric Catalytic Reduction with Transition Metal Complexes. II. Asymmetric Catalysis by a Supported Chiral Rhodium Complex, J. Am. Chem. Soc., 95 (1973) 8295-8299. 

Dumont W, Poulin JC, Dang TP, Kagan HB. Asymmetric catalytic reduction with transition metal complexes. II. Asymmetric catalysis by a supported chiral rhodium complex. J. Am. Chem. Soc. 1973 95(25) 8295-8299. 

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

Some general reviews on hydrogenation using transition metal complexes that have appeared within the last five years are listed (4-7), as well as general reviews on asymmetric hydrogenation (8-10) and some dealing specifically with chiral rhodium-phosphine catalysts (11-13). The topic of catalysis by supported transition metal complexes has also been well reviewed (6, 14-29), and reviews on molecular metal cluster systems, that include aspects of catalytic hydrogenations, have appeared (30-34). 

Electron spin resonance (ESR) signals, detected from phosphinated polystyrene-supported cationic rhodium catalysts both before and after use (for olefinic and ketonic substrates), have been attributed to the presence of rhodium(II) species (348). The extent of catalysis by such species generally is uncertain, although the activity of one system involving RhCls /phosphinated polystyrene has been attributed to rho-dium(II) (349). Rhodium(II) phosphine complexes have been stabilized by steric effects (350), which could pertain to the polymer alternatively (351), disproportionation of rhodium(I) could lead to rhodium(II) [Eq. (61)]. The accompanying isolated metal atoms in this case offer a potential source of ESR signals as well as the catalysis. 

---