Hydroformylation immobilizing catalysts

Using the hydroformylation of various olefins a variety of olefins was tested with the triisooctylamine-TPPTS salt [12, 13]. It could be shown that different olefmic compounds and structures (cycloaliphatic, internal, functionalized) can be used with the re-immobilized catalyst system (see Table 2). 

Tricyclodecane dialdehyde (TCD-dial) the starting product for TCD-diamine, is formed by hydroformylation of dicyclopentadiene, DCP. This hydroformylation was used as a test reaction for re-immobilized catalysts in membrane techniques (eq. (6)). 

Fig. 12.11. Rhodium complex used to generate an immobilized catalyst for continuous flow hydroformylation in 5CCO2.

Such a bell-like dependence of Wsp on the surface density of transition metal ions has also been observed in other catalytic reactions (hydroformylation, oxidation, polymerization, etc.), and is probably one of the specific features of catalysis by immobilized metal complexes. While there is no well-founded explanation of the rising branch of the plot, the diminishing trend may be coimected with the formation and fiirther growth of low- and/or zero-valent transition metal ion associations, diminishing the catalytic efficiency. Active centers of immobilized catalysts are localized on the boimdaries of cluster-like substances with stabilization by their electron systems. 

This reaction may be achieved by the use of two monofunctional catalysts (hydroformylation and hydrogenation) or one bifunctional catalyst (chloromethyl-ated CSDVB, modified by secondary amino groups with bound RhCl(PPh3)2(CO)) (Fig. 12-13). The rates of the first, second and third stages of the bifunctional catalyst are 5-, 15- and 30-fold higher respectively than those of the two monofunctional immobilized catalysts. We should also mention the oligomerization of butadiene with the hydroformylation of vinyl cyclohexene by Ni-Rh complexes bound to phosphorylated CSDVB and the preparation of 4-methyl-2-pentanone on polymer-immobilized heterometallic complexes, etc. 

SCCO2 has also been used as a solvent with a silica-immobilized catalyst in metathesis reactions [25]. A heterogeneous catalytic process is developed, in which catalyst leaching is avoided but the reactivity is lower than when using a homogeneous catalyst This application has also been extended to continuous-flow processes for hydrogenation [26], Friedel-Crafts alkylations [27], etherification [28], and hydroformylation [29] reactions. 

On the mesoporous material MCM-41, immobilized catalysts (compare Scheme 2.165) were tested in the multiple hydroformylation of 1-octene and reused for eight cycles [35]. With MCM-41 (R = Mes), in the first two cycles 80% of aldehyde formation was registered. Up to 20 ppm rhodium leaching was observed in the first catalytic cycle, but there was no loss in the fourth and eighth cycles. In the beginning, also 20% of the corresponding alcohol was found, but as more runs were performed the formation of the latter decreased (up to 2%). Simultaneously, the yields of aldehydes increased (up to >99% in run 3). The catalyst showed an initial linear selectivity of 1.9, which decreased in run 8 to 1.1. This decrease was attributed to the change in the microstructure of MCM-41 due to the harsh reaction conditions. With MCM-41 (R = fBu), formation of aldehyde remained stable over all runs (95->99%) and reduction to the alcohol was only... 

By comparison with the non-immobilized catalyst, similar reaction rates in the hydroformylation of 1-hexene were noted. By ultrafiltration on an asymmetric polyethersulfone membrane, the catalyst could be repeatedly recycled with 2-7% loss of rhodium. 

An obvious way to combine the advantages of homogeneous and heterogeneous catalysis for optimized hydroformylation catalysis is to covalently anchor the molecular catalyst complex to a solid surface. Such an immobilized catalyst could be used in fixed bed or slurry type reactors and product separation would be as straightforward as for any heterogeneous catalyst. Indeed, this approach has been most widely studied as evidenced by numerous academic papers and patents, reviews, and books (Keim and Driessen-Hoelscher, 1999 and Reek et cd., 2006). 

The distillation process is particularly suitable in the cases where the products are miscible with the ionic hquid, as in the case of the Rh-catalyzed hydroformylation of methyl-3-pentenoate in which the reaction mixture is monophasic. The use of an ionic hquid as a solvent results in the almost complete retention of the regioselec-tivity, whicdi is influenced by the ligand, and in significant enhancement of the lifetime and overall productivity of the catalyst. The catalyst recycling and product isolation were achieved by a distillation process under reaction conditions. In these cases, the immobilized catalyst is stabilized by the ionic hquid under the thermal stress of the distihation. The catalyst can be reused several times without additional regeneration process and without loss in activity and selectivity [12]. 

Gompared to other wide-bite-angle diphosphine ligands, xantphos-type ligands can be modified easily while retaining their favorable properties, especially in hydroformylation, and as a result many derivatives have been synthesized by several groups and used in fluorous-phase hydroformylation catalysis, aqueous phase catalysis, one-phase hydroformylation and catalyst extraction, catalysis in ionic liquids, hydroformylation with immobilized catalysts, and catalysis in supercritical G02. ... 

To date, these functionalized ligands have been investigated on the laboratory scale, in batch operations to immobilize rhodium catalyst in hydroformylation. 

Experimental evidence of the —S03" H0Si— interaction have been obtained from IR, Rh K-edge EXAFS, and CP MAS 3 IP NMR studies. These supported catalysts have been tested for the hydrogenation and hydroformylation of alkenes. No Rh leaching was observed.128-130 An extension to the immobilization of chiral metal complexes for asymmetric hydrogenation is reported below. 

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