Pillared Cobalt-Amino Acid Framework Catalysis for Styrene Carbonate Synthesis from CO2 and Epoxide by Metal-Sulfonate-Halide Synergism

The sulfonate anion is proposed as a remarkable partaker in catalyzing epoxide-CO2 cycloaddition for cyclic carbonate synthesis. The role is illustrated by the concerted action of a sulfonate-rich cobalt-amino acid framework catalyst [{Co(4,4-bipy)(L-cys)(H2O)}H2O](n) (2D-CCB) and a quaternary ammonium bromide co-catalyst in synthesizing styrene carbonate (SC) at a turnover number of 228. SC yield at atmospheric pressure is presumed to result from the activation of CO2 by the sulfonate group. The involvement of SO3- anions as basic sites in 2D-CCB is ascertained from the initial rate (r(0)) for catalyzing Knoevenagel condensation reactions and by using CO2 temperature programmed desorption. Microwave pulses are used for synthesizing 2D-CCB at a rate that is 288-fold faster than conventionally employed solvothermal methods. Unambiguous evidence for the pulsating role-play of sulfonate groups in 2D-CCB is perceived by comparing the activity of an analogous metal organic framework (3D-CCB) in which the sulfonate oxyanions are jammed by coordination with cobalt. 2D-CCB is analyzed for heterogeneity, and reused four times.