Synergetic Effect of Randomly Methylated β-Cyclodextrin and a Supramolecular Hydrogel in Rh-Catalyzed Hydroformylation of Higher Olefins

A significant improvement in Rh-catalyzed hydroformylation of very hydrophobic alkenes was achieved using a biphasic catalytic system consisting of a substrate-containing organic phase and a catalyst-containing hydrogel phase [consisting of poly(ethylene glycol) 20000 (PEG20000) and alpha-cyclodextrin (alpha-CD)]. The catalytic performance of the Pickering emulsion that resulted from the formation of alpha-CD/PEG20000 crystallites at the oil droplet surface proved to be greatly dependent upon the presence of additives. We showed that controlled uploads of randomly methylated beta-cyclodextrin (RAME-beta-CD) within the supramolecular hydrogel could positively affect both the catalytic activity and chemoselectivity of the hydroformylation reaction. Conversely, no Pickering emulsion could be observed using excess RAME-beta-CD, resulting in the subsequent degradation of the catalytic performance. Optical microscopy and optical fluorescence microscopy supported the catalytic results and allowed us to explain the role of RAME-beta-CD. Indeed, controlled uploads of RAME-beta-CD prevented the saturation of the oil droplet surface. RAME-beta-CD acted as a fluidifier of the Pickering emulsion and accelerated the dynamics of exchange between the substrate-containing organic phase and the catalyst-containing hydrogel phase. Morever, RAME-beta-CD acted as a receptor that participated in the conversion of the alkene by supramolecular means.