Hydroformylation and Carbonylation Reactions in Ionic Liquids

As mentioned above, the poor solubility of higher olefins in water still hampers their hydroformylation in aqueous media. Since 2003, ILs have entered the hydroformylation field as an alternative to the aqueous phase thanks to the higher solubilities of long-chain olefins in these non-conventional solvents. 

Since the pioneering results by Chauvin et al. in 1995,the story of the struggle against problems such as catalyst leaching, deactivation, etc., working in ILs, has been excellently outlined in a review by Haumann and Riisager.  

The use of triphenylphosphine as ligand led to acceptable rates in ILs, but with high rhodium leaching into the organic phase. Recourse to sulfonated phosphines such as monosulfonated triphenylphosphine retained the catalyst in the ionic liquid phase but decreased its activity significantly. This drawback was surmounted by the use of 47 (Table 1.5), which was derived from a simple cation metathesis reaction between TPPTS (37) and 1-butyl-2,3-dimethylimi-dazolium chloride [bdmim][Cl] in acetonitrile. 

The known cobaltocenium complexes 48 and 49 were proposed as ligands for rhodium (Table 1.5). They conferred a lower activity to the catalyst, but Rh leaching was less than 0.2% for both ionic ligands, and recycling experiments showed unchanged activity and selectivity for several runs. 

The concept of ionic tagging in aryl phosphine design is made explicit by the structures of ligands collected in Table 1.5. 

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