Influence of Oxidation State on the Catalytic Activity of Iron Catalysts for CO₂ Fixation to Cyclic Carbonates

In this work, one-component iron catalysts for the atom-economical reaction of CO₂ with epoxides have been used as efficient catalysts for the carbon dioxide cycloaddition into cyclic carbonates in excellent yields. These iron compounds showed high activity for the cycloaddition of CO₂ and different epoxides under 60-80 °C and 1 atm of CO₂. These systems constitute rare examples of bimetallic iron catalysts capable of efficiently promoting cyclic carbonate formation under mild, solvent-free conditions without requiring the use of external additives. Iron(III) compounds have shown greater catalytic activity than iron(II) analogs, highlighting the importance of the Lewis acid capacity of the metal center for epoxide activation. Very interestingly, the kinetics data demonstrate apparent first-order with respect to the catalyst, which supports synergic intramolecular cooperation between centers.