Use of ordered mesoporous materials as tools for organic and bioorganic synthesis

Abstract

Ordered mesoporous materials are materials with well defined pore sizes in the range of 2 to 50 nm. This paper shows that suspensions of particles of mesoporous materials can be useful tools for organic and bioorganic synthesis. They can be used to overcome reactant incompatibility, as is demonstrated for a reaction between 4-tert-butylbenzyl bromide and KI. The pores are impregnated with an aqueous solution of KI and the lipophilic reactant is present in the continuous apolar phase. The reaction occurs at the pore openings. The pores of the mesoporous material can also be used as host for a homogeneous catalyst. The catalyst-loaded particles are kept as a suspension in a medium that contains the reactants. This principle is demonstrated for a Heck-type reaction with a watersoluble rhodium catalyst inserted into the pores of mesoporous silica. It is also shown to work well for a 1,4-conjugate addition between two water-soluble reactants, 4-carboxyphenylboronic acid and methyl acrylate, in which case a toluene-soluble rhodium catalyst was entrapped in the pores of hydrophobized mesoporous silica. The same principle was also used for biocatalysis. Lipase was inserted into either hydrophilic or hydrophobic pores and used for both ester synthesis and ester hydrolysis. Finally, palladium nanoparticles were deposited inside the pores of mesoporous carbon and used as catalyst for a Sonogashira reaction.

Recent advances in Sonogashira reactions

“…Furthermore, palladium nanoparticles generated by reduction of palladium(II) chloride with sodium borohydride have been deposited on mesoporous carbon formed by pyrolysis of a polymer-coated silica template, this palladium-containing material being used as catalyst in the cross-coupling of iodobenzene and phenylacetylene. 288 The coupling was performed in the presence of sodium acetate in aqueous DMF as solvent, but the yield of diphenylacetylene obtained was just a 48% with deactivation of the catalyst by formation of large polydisperse crystalline palladium particles.…”

Mesoporous silica-supported rhodium complexes alongside organic functional groups for catalysing the 1,4-addition reaction of arylboronic acid in water

“…developed various novel homo- and heterogeneous Rh catalysts that catalysed 1,4-addition reactions in organic and aqueous solvents. 8,9 Our group also reported a cooperative catalytic system, wherein the Rh complex and tertiary amine were co-immobilized on the surface of silica to catalyse 1,4-addition reactions. 10 This report demonstrates the combination of supported Rh complex and co-immobilized tertiary amine group for efficient catalysis in organic solvent.…”