Electronic Tuning of Zinc Porphyrin Catalysts for the Conversion of Epoxides and Carbon Dioxide into Cyclic Carbonates

Bifunctional Zn^II porphyrin catalysts bearing tributylammonium bromide groups at the meta positions of the meso-phenyl groups showed high catalytic activity for the synthesis of cyclic carbonates from epoxides and CO₂. Herein, several substituents with different electronic properties were introduced at the para positions. Introduction of electron-donating groups decreased the catalytic activity, whereas the introduction of electron-withdrawing groups increased the activity. The substituents modulated the Lewis acidity of the zinc center, which was confirmed by binding constant experiments. The bifunctional catalyst bearing cyano groups showed the highest catalytic activity with a turnover frequency of up to 42 000 h⁻¹.