Sulfonated xantphos ligand and methylated cyclodextrin: A winning combination for rhodium-catalyzed hydroformylation of higher olefins in aqueous medium

The potential of sulfonated xantphos as ligand for a cyclodextrin-based hydroformylation process has been investigated. In addition to an activity enhancement, an increase in the linear to branched aldehydes ratio was measured when randomly methylated alpha- or P-cyclodextrins were used as inverse phase-transfer catalysts. The improvement of the selectivity was the result of two combined effects. First, contrary to what was observed with the TPPTS or TPPMS ligands, the interactions between the sulfonated xantphos and the methylated cyclodextrins were too weak to induce dissociation of the ligand from the complex under hydroformylation conditions. Second, concurrently to the constraint generated by the bulky sulfoxantphos ligand, the additional steric stress of the cyclodextrin cavity on the substrate compelled the latter to react preferentially by its terminal carbon, leading to very high regioselectivity toward linear aldehyde.