Hydroformylation polymer-bound soluble catalyst

For ultrafiltration as a unit operation for the separation of polymer-bound soluble catalysts in particular, the recovery process for a rhodium catalyst from the hydroformylation of dicyclopentadiene is an illustrative example (for another detailed example, see Section 7.5) [26, 27]. Toluene can be used as a solvent with the polyaramide membrane employed. TPPTS or also a sulfonated bidentate phosphine with large ammonium counterions, are used as ligands. For efficient recovery, molecular weights of the catalyst of more than 3000 g mofi were required on the membrane used. Separation is performed in two steps [28]. A pilot plant was run successfully over an extended period of time of three months. 

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 . ... 

Industrial interest in soluble polymer-bound catalysts has been closely linked to the development of ultrafiltration membranes with sufficient long-term stability in organic solvents. Membranes fulfilling these requirements were prepared first in the late 1980s. Today, solvent-stable flat sheet membranes and membrane modules are available from several suppliers. As for the viability of ultrafiltration in organic solvents, rhodium-catalyzed hydroformylation of dicydopentadiene with continuous catalyst recovery and recycling has been demonstrated successfully on a pilot plant scale over an extended period of time [5]. The synthesis of other fine chemicals by asymmetric reduction and other reactions has also been carried out in continuously operated membrane reactors (also cf Section 7.5) [6-9]. The extent of commercial interest in catalysts bound to soluble polymers appears to fluctuate at intervals. Amongst other factors, the price of precious metals can be a driver. 

The use of soluble polymers as catalysts was also explored by Bayer. His group showed that both diphenylphosphinated polystyrene and diphenylphosphinated poly(ethylene glycol) could be used as recoverable, reusable hydroformylation catalysts. Separation of the catalyst and the reaction products in these cases was achieved by taking advantage of the properties of the polymer chain. Solvent precipitation or membrane filtration both proved to be acceptable techniques to isolate products free from the polymer-bound catalyst. 

Pentene was hydroformylated to Cg aldehydes at 22 °C under 0.1 MPa H2/CO. The reaction solution was membrane-filtered and the products (77% n-hexanal and 23% methylpentanal) were analyzed by GC. The retained catalyst could be recycled twice [3], Along with Ohkubo et al, Bayer and Schurig also reported on soluble polymers as supports for asymmetric catalytic systems. The soluble polystyrene-bound analogue of DlOP (4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-l,3-dioxalane) was used for the asymmetric Rh-catalyzed hydroformylation of styrene but the ee of the predominantly obtained branched product was only 2% [Eq. (2)]. 

Hydroform ylation catalysts based on soluble organic polymers have also been described in the patent literature (55). For example, Trevillyan has reported using a polyphenylene-bound diphenylphosphine ligand to form a tertiary phosphine cobalt carbonyl complex useful in hydroformylation of 1-octene to mainly nonanal and 2-methyloctanal. 

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