Eco-friendly solvents and amphiphilic catalytic polyoxometalate nanoparticles: a winning combination for olefin epoxidation

Eighteen eco-friendly solvents were examined to carry out the epoxidation of olefins with the amphiphilic catalytic dodecyltrimethylammonium polyoxometalate nanoparticles [C-12](3)[PW12O40] in comparison with [H](3)[PW12O40] and [Na](3)[PW12O40]. Surprisingly, the screening of solvents with cyclooctene has revealed that the [C-12](3)[PW12O40] catalyst is much more active with initial turn-over frequencies, TOF0, increasing up to a factor of 10. Moreover, the reaction occurs at competitive rates in four relevant solvents, i.e. cyclopentyl methyl ether, 2-methyl tetrahydrofuran, methyl acetate and glycerol triacetate, for which TOF0 values are higher than 260 h(-1). The recyclability of the systems is demonstrated and the scope of substrates has been successfully extended to cyclohexene, 1-octene, limonene, 3-carene, alpha-pinene, beta-pinene and neryl acetate with good epoxide selectivity. The catalytic performances in the green solvent are assigned to the formation of stable [C-12](3)[PW12O40] nanoparticle dispersions which have been characterized by transmission electron microscopy and dynamic and multiple light scattering experiments. Finally, the Kamlet-Taft parameters were measured in order to correlate the physicochemical properties of the solvents and the catalytic activity.