Hydroformylation catalysts, selective

Conventional triorganophosphite ligands, such as triphenylphosphite, form highly active hydroformylation catalysts (95—99) however, they suffer from poor durabiUty because of decomposition. Diorganophosphite-modified rhodium catalysts (94,100,101), have overcome this stabiUty deficiency and provide a low pressure, rhodium catalyzed process for the hydroformylation of low reactivity olefins, thus making lower cost amyl alcohols from butenes readily accessible. The new diorganophosphite-modified rhodium catalysts increase hydroformylation rates by more than 100 times and provide selectivities not available with standard phosphine catalysts. For example, hydroformylation of 2-butene with l,l -biphenyl-2,2 -diyl... 

Selective Hydroformylation Catalysts Through Self-Assembly. 157... 

Abu-Reziq, R., Alper, H., Wang, D.S. and Post, M.L. (2006) Metal supported on dendronized magnetic nanopartides highly selective hydroformylation catalysts. Journal of the American Chemical Society, 128 (15), 5279-5282. 

One of the most selective hydroformylation catalysts was obtained when cobalt acetate was irradiated in the presence of an excess of a phosphine, with synthesis gas at 80 atm, in methanol as the solvent. Propylene was hydroformylated with this catalyst to give butyraldehyde with an n/i ratio of more than 99/1 /10/. In the absence of phosphine, the cobalt acetate forms a more active catalyst which is, however, less selective for straight chain products /23/. 

It is interesting to note that using the sol-gel procedure (I) the pre-formation of the rhodium diphosphine complex suppressed the formation of ligand free rhodium-cations on the silica surface. This approach gave rise to a well-defined, very selective hydroformylation catalyst. All immobilised catalysts were 10 to 40 times slower than the homogeneous catalyst under the same conditions, the sol-gel procedure yielding the fastest catalyst of this series. 

However, (Ph3P)2Rh(CO)Cl on alumina or activated carbon were effective hydroformylation catalysts under more severe conditions 108). At 148°C and a pressure of 49 atm (CO 37.5 mol%, H2 37.5, propylene 25), good activity was found. The propylene conversion was 30% at a contact time of 0.92 cm3 of reactor void space/cm3 of feed per minute. Isomer ratios of 1.3 to 1.9 1 n iso were realized. By-product formation was low, with <1% conversion to alcohols plus alkanes and 2.2% high-boiling materials. This system was stable for a 300 hour operating time, with no detectable loss of activity or selectivity. 

More recently, during research aimed at supporting the highly linear selective hydroformylation catalyst [Rh(H)(Xantphos)(CO)2] onto a silica support, the presence of a cationic rhodium precursor in equilibrium with the desired rhodium hydride hydroformylation catalyst was observed. The presence of this complex gave the resulting catalyst considerable hydrogenation activity such that high yields of linear nonanol could be obtained from oct-1-ene by domino hy-droformylation-reduction reaction [75]. 

Hydrosilylation of allyl chloride with HSiCl3 leads to Cl(CH2)3SiCl3 that can be used for many surface modifications after substitution of the chlorides by suitable functional groups [5], For instance it can be used to anchor soluble hydroformylation catalysts to a silica surface (Figure 18.3). Many examples have been reported and we present only one example of a selective Xantphos type ligand [6],... 

The important criteria for catalyst selection in the hydroformylation of FAMEs are activity, stability and catalyst-product separation. For this process, the feed is... 

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

Applying P-31 NMR to the field of hydroformylation catalysis by triphenylphosphine rhodium complex-based systems is the subject of this chapter. These hydroformylation catalyst systems are of high academic and technological interest. They are effective for hydroformylat-ing 1-olefins at low pressure and temperature and exhibit a high selectivity to n-aldehydes ... 

As indicated in the introduction, bis-l,3-diphenylphosphino-propane (dppp) and bis-l,2-diphenylphosphinoethane (dppe) were reacted with tris(triphenylphosphine)rhodium(II) carbonyl hydride in toluene-deuterobenzene solution to derive cis-chelate complex hydroformylation catalysts. These complexes were expectedly non-selective terminal hydroformylation catalysts for 1-butene hydroformylation (see Table I) because of their cis-stereochemistry. They were also somewhat less active due to their specific structural features. The structure of these complexes in solution was studied in detail by P-31 NMR spectroscopy. 

The high stability of the bicyclic complexes in such systems and their cis-stereochemistry are suggested to explain their low activity and lack of selectivity as hydroformylation catalysts when compared with similar systems based on triphenylphosphine. 

The hydroformylation of olefins is one of the largest and most prominent industrial catalytic processes, producing millions of tons of aldehydes annually [102]. Initially, cobalt-carbonyl species were used as catalyst, though rhodium complexes modified by special ligands, usually phosphines, are predominantly used nowadays. Over the last two decades, continued development of new phosphine and phosphite ligands has allowed significant advances in hydroformylation chemistry, especially with respect to catalyst selectivity and stability [103]. 

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