Water-soluble phosphane-substituted cyclodextrin as an effective bifunctional additive in hydroformylation of higher olefins

In cyclodextrin (CD) -mediated aqueous biphasic catalysis, favoring contacts between the CD ("host"), the organic substrate ("guest") and the water-soluble catalyst is crucial for the reaction to proceed efficiently at the aqueous/organic interface. Grafting the catalyst onto the CD backbone thus appears as an attractive approach to favor the molecular recognition of the substrate and its subsequent catalytic conversion into products. In this context, a new water-soluble beta-CD-based phosphane was synthesized and characterized by NMR, tensiometric and ITC measurements. The beta-CD-based phosphane consisted of a 3,3'-disulfonatodiphenyl phosphane connected to the primary face of ii-CD by a dimethyleneamino spacer. Intra-and intermolecular inclusion processes of one of the two sulfophenyl groups into the beta-CD cavity were identified in water. However, the association constant (K-a) related to the beta-CD/sulfophenyl group couple was low. Accordingly, the inclusion process was easily displaced upon coordination to rhodium complexes. The efficacy of the resulting Rh-complex coordinated by beta-CD-based phosphanes was assessed in Rh catalyzed hydroformylation of higher olefins. The catalytic system proved to be far more successful and efficient than a system consisting of supramolecularly interacting phosphanes and CDs. The catalytic activity was up to 30-fold higher while the chemo-and regioselectivities remain rather unchanged.