1,4-Conjugate addition reaction catalyzed by a homogeneous rhodium catalyst entrapped in hydrophobized ordered mesoporous silica

A 1,4-conjugate addition reaction between p-carboxyphenylboronic acid and methyl acrylate has been performed using a homogenous rhodium catalyst entrapped in the hydrophobic pores of hydrophobized ordered mesoporous silica. The catalyst-loaded inorganic particles were dispersed in an aqueous solution containing the reactants. The yields obtained were higher than that obtained in the conventional liquid–liquid two-phase system. From the recycling experiments it was demonstrated that with hydrophobized ordered mesoporous silica as support a catalytic activity extending over several consecutive runs compared to the liquid–liquid two-phase system could be obtained. The major advantage with having the catalyst “heterogenized” by entrapment into the siliceous material is the simplicity of the work-up process. The porous particles, containing the catalyst, are simply removed by filtration after completed reaction and the product precipitated from water upon acidification.