Efficient solvent-free fixation of CO2 into cyclic carbonates catalyzed by Bi(III) porphyrin/TBAI at atmospheric pressure

Abstract

A series of Bi (III) porphyrin complexes were synthesized and tested as catalysts for chemical fixation of carbon dioxide (CO2) and epoxides under solvent-free conditions in the presence of tetrabutylammonium iodide (TBAI) as co-catalyst. The influences of various factors (catalyst systems, catalyst amount, pressure, time, and temperature) on the catalytic activities have been studied systematically. The catalytic performances were strongly influenced by the substitute of porphyrin framework and axial group X−. 2a/TBAI was screened as the most active catalyst system under the optimized conditions (90°C, 1h, 2MPa). Notably, a very high turnover frequency (TOF) value (37,900h−1) for catalyst 2a was achieved via adjusting reaction factors. This binary catalytic system also exhibited good activities (up to 98%) and selectivities (>99%) for the cycloaddition reaction of many epoxides, including diepoxides, with CO2 into corresponding cyclic carbonates at atmospheric pressure (0.1MPa) within 6h. Especially, the glycidyl methacrylate, which is known to have the self-polymerization tendency at higher temperature, could be converted into its corresponding cyclic carbonate selectively with high yield of 94.8% with 2a/TBAI as catalyst at room temperature and 0.1MPa. In spite of the homogeneous property of the catalytic system, 2a/TBAI, could maintain the high performance under atmospheric pressure for 60h, or even longer. Moreover, kinetic studies gave out an inferred mechanism.