Lewis acid improved dioxygen activation by a non-heme iron(II) complex towards tryptophan 2,3-dioxygenase activity for olefin oxygenation.

Dioxygen activation and catalysis around ambient temperature is a long-standing challenge in chemistry. Inspired by the significant roles of the hydrogen bond network in dioxygen activation and catalysis by redox enzymes, this work presents a Lewis acid improved dioxygen activation by an Fe(BPMEN)(OTf) complex towards tryptophan 2,3-dioxygenase (TDO) activity for 3-methylindole and common olefinic CC  bond oxygenation and cleavage (enzymatic Brønsted acid chemical Lewis acid). It was found that the presence of a Lewis acid such as Sc could substantially improve olefinic CC  bond oxygenation and cleavage activity through Fe(BPMEN)(OTf) catalyzed dioxygen activation. Notably, a more negative value in the Hammett plot of -substituted styrene oxygenations was observed in the presence of a stronger Lewis acid, disclosing the enhanced electrophilic oxygenation capability of the putative iron(III) superoxo species through its electrostatic interaction with a stronger Lewis acid. Thereof, this work has demonstrated a new strategy in catalyst design for dioxygen activation and catalysis for olefin oxygenation, a significant process in the chemical industry.