Polymer-bound catalysts hydroformylation

Allen (106) also studied cobalt hydroformylation with a polymer-bound catalyst. The polymer was formed from diphenyl-p-styrylphosphine cross-linked with divinylbenzene. 2-Hexene was the substrate, and reaction conditions were 175°C and 1500-3000 psi of 1/1 H2/CO. The product aldehyde was 55% linear, and the effluent product solution contained 20-50 ppm cobalt. 

Hydroformylation of 1-hexene was studied at 80 °C under 30 bar of CO/H2 (1 1) with the in-situ generated catalyst 7. The reaction was monitored via the CO/H2-uptake which was measured with mass flow meters. The polymer-bound catalysts possessed moderate activities in methanol (200-400 TO/h), and the activity was approx. 4-times higher when non polymer-bound TPPMS was used as the ligand. The activity of the catalyst 7 decreased in recycling experiments (entries 2a-2b in Table 2), which can presumably be attributed to a partial oxidation of the phosphine ligands. Moreover, the activity of the complex was not significantly affected by the change of P Rh... 

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. 

The polymers were converted to supported catalysts corresponding to homogeneous complexes of cobalt, rhodium and titanium. The cobalt catalyst exhibited no reactivity in a Fischer-Tropsch reaction, but was effective in promoting hydroformylation, as was a rhodium analog. A polymer bound titanocene catalyst maintained as much as a 40-fold activity over homogeneous titanocene in hydrogenations. The enhanced activity indicated better site isolation even without crosslinking. 

Table 2 Hydroformylation of 1-hexene with polymer-bound Rh phosphine catalyst 7a...

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. 

Monomeric or polymer-bound C0CI2 is an active acetalization and transac-etalization catalyst [17]. Its efficiency can be improved by the addition of chlorotrimethylsilane [18]. Also, Co2(CO)g or heterogeneous Co catalysts convert olefins in the presence of alcohols into acetals [19, 20]. HCo(CO)4, a typical hydroformylation catalyst and strong acid, is able to reduce under hydroformylation conditions (CO/H2 = 2 l, about 165bar, 160-210°C) acetals of aromatic aldehydes into the corresponding ethers. Interestingly, acetals of aliphatic aldehydes did not react under these conditions. 

Hydroformylation Catalysts Based on Polymer-Bound Transition Metal Complexes... 

The highly important hydroformylation of olefins to aldehydes is a fruitful area for the development and application of new techniques. Photochemically initiated high-pressure formylation and the use of polymer-bound ruthenium catalysts are but two examples. The complex role of HCo(CO)4 in hydroformylation has been reviewed. Nickel(O) complexes catalyse an acetylation of aryl... 

Since the mid-1990s, most studies of polymer-related hydroformylation have involved the use of polymer-bound rhodium catalysts for the hydroformylation of small molecule olefins. However, a few recent papers have focused on the catalytic hydroformylation of high-molecular-weight polymers [previously, formyl loading higher than 50% had not been... 

Various transition metal catalysts, including those based on Rh, Pt, Pd, Co, and Ti, have been bound to polymer supports—mainly through the phosphenation reaction described by Eq. 9-65 for polystyrene but also including other polymers, such as silica and cellulose, and also through other reactions (e.g., alkylation of titanocene by chloromethylated polystyrene). Transition-metal polymer catalysts have been studied in hydrogenation, hydroformylation, and hydrosilation reactions [Chauvin et al., 1977 Mathur et al., 1980]. 

Relatively few hydroformylations using supported cobalt complexes have been reported. Moffat (78, 79) showed that poly-2-vinylpyridine reversibly reacted with both Co2(CO) and HCo(CO)4, the cobalt carbonyl being displaced by excess carbon monoxide. This enabled the polymer to pick up the cobalt carbonyl at the end of the reaction and, thus, allowed it to be separated from the products by filtration. The polymer acted as a catalyst reservoir by rapidly releasing the cobalt carbonyl into solution in the presence of further carbon monoxide, so that the actual catalysis was a homogeneous process. More recently, cobalt carbonyl has been irreversibly bound to a polystyrene resin... 

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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