Carbon Dioxide Fixation by Cycloaddition with Epoxides, Catalyzed by Biomimetic Metalloporphyrins

Several biomimetic metalloporphyrin complexes (M(TPP)XY; in which TPP=meso-porphyrin; M=MgII, AlIII, SnII, or SnIV; X=OAc, F, Cl, Br, I, OTf, or none; and Y=Cl, Br, I, OTf, or none) were prepared, characterized, and used effectively in the green synthesis of cyclic carbonates from epoxides and CO2. The catalytic systems of Mg(TPP)/tetrabutylammonium iodide and Al(TPP)Cl/phenyltrimethyl ammonium tribromide can initiate the cycloaddition of epoxides and CO2 at room temperature to generating cyclic carbonates in excellent yield. Chlorophyll A is shown to induce enantioselectivity of racemic propylene oxide. All reactions displayed excellent selectivity to cyclic carbonate without polycarbonate and other by-products. Chloropropylene carbonate is shown to be obtained under CO2 bubbling conditions catalyzed by Al(TPP)Cl/phenyltrimethylammonium tribromide. The catalytic order of activity for biomimetic metalloporphyrins is AlIII>MgII>SnIV>SnII. These phenomena are explained with respect to the Lewis acidity of metal center in metalloporphyrins.