Cationic Zn-Porphyrin Immobilized in Mesoporous Silicas as Bifunctional Catalyst for CO₂ Cycloaddition Reaction under Cocatalyst Free Conditions

Abstract

Immobilization of metalloporphyrin onto a solid support is highly desirable in the chemical industry. Herein, we reported for the first time the efficient immobilization of cationic zincporphyrin complexes on mesoporous SBA-15 by a simple one-pot method by refluxing 5,10,15,20-tetrakis(4-pyridyl)porphyrin zinc(II) (Zn-TPy), SBA-15, and 3-(trimethoxysilyl)propyl bromide in toluene, DMF, NMP, or THF. Studies suggest that solid catalyst with high Zn content, stiochiometric Br–/Zn ratio, and uniform distribution of active sites could be obtained using DMF as the solvent, possibly related to its suitable polarity. The bifunctional solid material with both Lewis acid site and nucleophile acts as an efficient catalyst for catalyzing cycloaddition of CO2 and epoxides under cocatalyst free conditions. Compared with the homogeneous counterpart, the solid catalyst is more active (TOF = 1686 h–1 versus 370 h–1). This suggests that the closely connected Lewis acid and Br– in the solid material could enhance their cooperation during the catalytic process. This work provides an efficient method for the synthesis of bifunctional solid catalyst exhibiting enhanced cooperation activation effect for the CO2 cycloaddition reaction.