Supported catalysts hydroformylation

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. 

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. 

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. 

In subsequent work the same supported catalysts were used in different reactor setups [20] (Figure 3.3). A vapour-phase reactor in which the supported catalyst was mounted on a bed was used for the hydroformylation of volatile alkenes such as cis-2-butene and trifluoropropene. The initial activities and selectivity s were similar to those of the homogeneous solutions, i.e. a TOF of 114 and 90% ee in the hydroformylation of trifluoropropene was reported. No rhodium was detected in the product phase, which means less then 0.8% of the loaded rhodium had leached. The results were, however, very sensitive to the conditions applied and, especially at longer reaction times, the catalyst decomposed. In a second approach the polymer supported complex was packed in a stainless steal column and installed in a continuous flow set-up. 

The existence of two different rhodium species co-existing on the silica support can be used as an advantage by controlling their relative amount. Under standard hydroformylation conditions, the cationic species and the neutral hydride complex are both present in significant amounts. Hence hydroformylation and hydrogenation will both proceed under a CO/H2 atmosphere. Indeed a clean one-pot reaction of 1-octene to 1-nonanol was performed, using the supported catalyst for a hydroformylation-hydrogenation cascade reaction. 98 % of the 1-octene was converted in the... 

Figure 3.6. Turn over number (TON) displayed as function of time for the hydroformylation of 1-octene using a set-up for continuous processes with SCCO2 as mobile phase and supported catalyst 2...

SLPC or SAPC (supported liquid [or aqueous] phase catalysis [9,10,62,64] see also Section 5.2.5) provide no improvement, probably because of the tremendous stress on the support/transition metal bond during the repeated change between tetrahedral and trigonal-bipyramidal metal carbonyls over the course of a single catalyst cycle. Only recent publications [11,21,26b,28h] report on successful realization of supported homogeneous hydroformylation catalysts, but so far there is no confirmation by practise-soriented tests -not to mention by commercial applications. 

Figure 9.2. Ligand used for supporting a hydroformylation catalyst on a solid support. Leaching of rhodium under the reaction conditions is insignificant.

The scope of SILP was extended by investigating charged monophosphine ligands, as well as liquid-phase CF hydroformylation. The latter was demonstrated on 1-octene using the SILP Rh-(NORBOS-Cs3)/ [bmim][PF6]/silica catalyst. The authors recognize that the supported catalyst-phihc phase offers the significant advantage of very efficient ionic liquid use. 

Keywords Carbonylation Homogeneous catalysis Hydroformylation Immobilisation Ionic liquids Supported catalysts... 

Alumina-supported catalysts prepared using the bimetallic carbonyl precursors showed a better performance in alkene hydroformylation than conventional Co-Rh catalysts. This was related to the presence of highly dispersed Rh-Co clusters with frames corresponding to that of the parent carbonyl-precursor that were characterized by EXAFS [140, 183]. Silica-supported bimetallic entities RhCo3,... 

Anchoring the catalyst to polymeric materials has some advantages in easy product separation and catalyst recovery for recycling. The first example of a polymer-supported rhodium catalyst for hydroformylation was reported in 1975. Since then, many reports have been published on polymer-supported catalysts here, we focus on examples of normal-sc QcxiY or enantioselective hydroformylation. 

Due to the heterogeneity of the recently advanced solid-support catalyst for the hydroformylation, direct structural information on catalyst surface has been collected by extended X-ray absorption fine structure (EXAFS). Iwasawa is the first to directly characterize the structure of dimeric rhodium complexes supported on... 

Both the rhodium and the cobalt complexes catalyze olefin isomerization as well as olefin hydroformylation. In the case of the rhodium(I) catalysts, the amount of isomerization decreases as the ligands are altered in the order CO > NR3 > S > PR3. When homogeneous and supported amine-rhodium complexes were compared, it was found that they both gave similar amounts of isomerization, whereas with the tertiary phosphine complexes the supported catalysts gave rather less olefin isomerization than their homogeneous counterparts (44, 45). 

Hydroformylations utilizing the polymer-supported catalysts showed comparable rates and gave nearly the same optical yield as the homogeneous analogue. Recovering of the cross-linked polymer was achieved by simple filtration with slight loss in activity but no loss in selectivity 93). 

Supported aqueous-phase catalysts can also be used to advantage. These supported catalysts have a thin aqueous film adhering to silica gel that contains the water-soluble complex (131). These catalysts are particularly useful for the hydroformylation of substrates such as oleyl alcohol (132). Since these catalytic reactions occur at the phase boundary, characteristics such as the water content can cause changes both in the reactivity and in the linear branched chain ratio of the product aldehyde. 

The soluble polymer-supported catalysts have also been used for asymmetrically catalyzed reactions Following a procedure for the preparation of insoluble polymeric chiral catalysts a soluble linear polystyrene-supported chiral rhodium catalyst has been prepared. This catalyst displays high enantiomeric selectivity compared to the low molecular weight catalyst. Thus, hydroformylation of styrene using this catalyst produces aldehydes in high yields. The branched chiral hy drotropaldehy de is formed in 95% selectivity. 

Propylene Hydroformylation over Various Metal Carbonyl Clusters Impregnated on Metal Oxides Compared with That over Conventional Rhodium Supported Catalyst"... 

Fig. 22. Catalytic performances of ZnO- and carbon-supported Rh, bimetallic RhCo, and Co carbonyl clusters [RhsICO),, Rh4, Co,(CO),2] for propene hydroformylation (C3H / CO/H2 ratio 1 1 I, total pressure 0.8 atm at I52°C). For specific rates, open circles relate to carbon-supported and filled circles to ZnO-supported catalysts. For n-isomer selectivities, open squares relate to carbon-supported and filled squares relate to ZnO-supported catalysts.

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