Correction to “Bifunctional Porphyrin Catalysts for the Synthesis of Cyclic Carbonates from Epoxides and CO2: Structural Optimization and Mechanistic Study”

Abstract

We prepared bifunctional MgII porphyrin catalysts 1 for the solvent-free synthesis of cyclic carbonates from epoxides and CO2. The activities of 1d, 1h, and 1i, which have Br–, Cl–, and I– counteranions, respectively, increased in the order 1i < 1h < 1d. Catalysts 1d and 1j–m, which bear four tetraalkylammonium bromide groups with different alkyl chain lengths, showed comparable but slightly different activities. Based on the excellent catalyst 1d, we synthesized MgII porphyrin 1o with eight tetraalkylammonium bromide groups, which showed even higher catalytic activity (turnover number, 138,000; turnover frequency, 19,000 h–1). The catalytic mechanism was studied by using 1d. The yields were nearly constant at initial CO2 pressures in the 1–6 MPa range, suggesting that CO2 was not involved in the rate-determining step in this pressure range. No reaction proceeded in supercritical CO2, probably because the epoxide (into which the catalyst dissolved) dissolved in and was diluted by the supercritical CO2. Ex...