Hydroformylation, asymmetric solvents

In 2000, better results were obtained by Bonnet et al. by using readily available chiral thioureas as new ligands in the asymmetric rhodium-catalysed hydroformylation of styrene. In general, the conversion of styrene and enantioselectivities were modest, but when the reaction was carried out in heptane as the solvent, an enantioselectivity of 41% ee was obtained (Scheme 10.6). 

The asymmetric hydroformylation of styrene and its derivatives is shown in Scheme 6-56. The results of the reaction are governed by several factors, such as solvent, temperature, reaction time, and configuration of the ligand. The configuration of the product, in turn, is governed mainly by the configuration of the phosphine moiety (compare Entries 1 and 5 in Scheme 6 56). Low temperature gives a better branched/linear ratio, as well as better enantioselectivity, but normally it leads to a drop in reaction rate. The reaction is sensitive to the... 

Perfluoroalkyl-substituted BINAPHOS ligand 29c was also developed for the asymmetric hydroformylation of vinyl arenes in SCCO2. With this ligand regio-and enantio-selectivity (ee s up to 93.6%) were high without the need for hazardous organic solvents [63,64],... 

There is very little information available on asymmetric hydroformylation in aqueous solutions or biphasic mixtures despite that asymmetric hydroformylation in organic solvents has long been studied very actively. This is even more surprising since enantioselective hydrogenation in aqueous media has been traditionally a focal point of aqueous organometallic catalysis and several water soluble phosphine ligands have been synthetized in enantiomerically pure form. 

Francio G, Leitner W (1999) Highly regio- and enantio-selective rhodium-catalysed asymmetric hydroformylation without organic solvents. Chem Commun 17 1663-1664... 

Shibahara F, Nozaki K, Hiyama T (2003) Solvent-free asymmetric olefin hydroformylation catalyzed by highly cross-linked polystyrene-supported (R, S)-BfNAPHOS-Rh(I) complex. J Am Chem Soc 125(28) 8555-8560... 

Hydroformylation reactions have been one of the most well researched areas of CO2 reaction chemistry. Hydroformylation reactions are necessary for the formulation of complex chemicals. The first complete kinetic study of a hydroformylation reaction was in CO2 and was first published in 1999. Prior to this, most studies had considered the effect of dense CO2 on linear branch ratios or other forms of selectivity. Carbon dioxide has an effect on the selectivity of a variety of hydroformylation reactions and can enhance the rate of reaction Hydroformylation is by its nature regioselective and typically the linear branch or n iso ratio is used as the measure of selectivity. The use of asymmetric catalysts to achieve chiral products has introduced a second degree of selectivity to catalyst design. Advancements in catalyst design, together with solvent selection, are expected to make... 

The use of ionic hquids in asymmetric catalysis was reported even later, beginning with Chauvin s report on a catalytic asymmetric hydrogenation and hydroformylation of alkenes in 1995 [125]. Since then, enantioselective catalysis in ionic hquids has attracted remarkable interest as an approach to the facile recycling of expensive chiral ligands and catalysts, and a range of enantioselective catalyhc transformahons have been examined in ionic liquids [126]. In many cases, ionic hquids have a beneficial effect on the achvihes and enanhoselectivities, and demonstrate facile recovery and reusabihty of the ionic solvent-catalyst systems. The reader is referred to Chapter 7 for an excehent review on the development of enanhoselechve catalysis in ionic hquids. 

Takaya and Nozaki invented an unsymmetrical phosphin-phosphite ligand, (R,S)-BINAPHOS, which was used in the Rh(l)-catalyzed asymmetric hydroformylation of a wide range of prochiral olefins, with excellent enantioselectivities [120, 155]. A highly crosslinked PS-supported fR,S)-BINAPHOS(257)-Rh(I) complex was prepared and applied to the same reaction (Scheme 3.83) [156]. Using the polymeric catalyst, the asymmetric hydroformylation of olefins was performed in the absence of organic solvents. The reaction of cis-2-butene, a gaseous substrate, provided (S -methylbutanal with 100% regioselectivity and 82% ee upon treatment with II, and CO in a batchwise reactor equipped with a fixed bed. 

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