Regioselective hydroformylation of vinylarenes in aqueous media by a sol–gel entrapped rhodium catalyst

Two methods for selective hydroformylation of vinylarenes in aqueous media are described. One method relies on the application of [Rh(cod)Cl]2 and a tertiary phosphane entrapped within an ionic liquid-confined silica sol–gel support. The second method utilizes the same rhodium compound, encaged within ionic-liquid-free hydrophobicized sol–gel. Both methods are best carried out at 50 °C in aqueous emulsions or microemulsions that consist of the substrate, a surfactant, a co-surfactant and >89% water. The optimal H2/CO ratio is between 1 and 1.1. Both methods allow the reuse of the heterogenized catalyst for several runs. While the regioselectivity and the yield are hardly affected by the electronic nature of the substrates, they are significantly dependent on the reaction temperature, on the surfactant employed, and on the hydrophobicity of the support of the catalyst. Despite the use of H2 in the reactions, no transformation of the organometallic catalyst into metallic nanoparticles could be detected.

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► Regioselective hydroformylation of vinylarenes to form branched aldehydes.
► Replacement of organic solvents by aqueous microemulsions.
► Elucidation of the factors that influence selective catalysis.