A metal-free porphyrin heterogenised onto SBA-15 silica: A performant material for the CO2 cycloaddition to epoxides and aziridines

The cycloaddition of CO 2 to epoxides, N -alkyl and N -aryl aziridines was efficiently promoted by TPPH 2 @SBA-15 heterogeneous catalyst in the presence of either TBAI or TBACl as the co-catalyst. Good catalytic performances were associated with an excellent recyclability of the promoter also in gram-scale syntheses. The covalently heterogenisation of a free-base porphyrin on SBA-15 silica yielded TPPH 2 @SBA-15 ( TPPH 2 = tetraphenyl porphyrin), which was very efficient to promote the CO 2 cycloaddition to three-membered rings. The TPPH 2 @SBA-15 /TBAX-based catalytic procedure was very general, as revealed by excellent activities registered in the reaction of CO 2 with epoxides, N -alkyl and N -aryl aziridines, forming cyclic carbonates, N -alkyl and N -aryl oxazolidinones, respectively. It is worth noting that this is the first example of the heterogeneously catalysed synthesis of N -aryl oxazolidinones from corresponding N -aryl aziridines. The scale-up of the methodology highlighted that catalytic performances of all the three investigated reactions were maintained also working at a gram-scale to pave the way for future developments of the procedure. In addition, the recycle of TPPH 2 @SBA–15 for several consecutive reactions was efficient and observed catalytic activities were very similar to those registered in the presence of a fresh material. All the acquired data indicated an excellent sustainability of the catalytic protocol to envisage upcoming practical applications.