Epoxidation of styrene with porphyrin catalysts encapsulated in molecular square cavities

Metalloporphyrins can catalyze the epoxidation of olefins under mild conditions. However, the use of these catalysts is limited because they are easily deactivated due to dimer formation. We have investigated a strategy to overcome this by encapsulating porphyrin catalysts within protective hosts known as "molecular squares," formed from metal corners and organic linkers. The host can prevent catalyst deactivation and induce reaction selectivity similar to the function the protein framework plays in an enzyme. Results will be presented from experimental kinetic studies, quantum chemical calculations, and microkinetic modeling. The quantum mechanical calculations were used to investigate the reaction mechanism of olefin epoxidation reactions with Mn-porphyrin catalysts. Five different possibilities have been proposed in the literature for a key intermediate. Our DFT results show that only two of them are reasonable candidates, and the calculations suggest a new "stepwise" reaction pathway that includes both of them in sequence.