Direct Observation of All Open-Shell Intermediates in a Photocatalytic Cycle

Abstract

Molecular photocatalysis has shown tremendous success in sustainable energy and chemical synthesis. However, visualizing the transient open-shell intermediates in photocatalysis is a significant and long-standing challenge. By employing our recently developed innovative time-resolved electron paramagnetic resonance technique, we directly observed all radicals and radical ions involved in the photocatalytic addition of pempidine to tert−butyl acrylate. The full picture of the photocatalytic cycle is vividly illustrated by the fine structures, chemical kinetics, and dynamic spin polarization of all open-shell intermediates directly observed in this prototypical system. Given the universality of this methodology, we believe it greatly empowers the research paradigm of direct observation in both photocatalysis and radical chemistry.

Reductive Cyclopropanation through Bismuth Photocatalysis

“…To this end, we provide here an unprecedented reductive C–C coupling catalyzed by Bi toward cyclopropanation, using alkyl diiodides and olefins (Figure B). The process is characterized by the ability of Bi to concatenate various mechanistic steps, through open-shell intermediates . Cyclopropanation is achieved through a series of (1) S N 2-type reaction to C(sp 3 )–I; (2) homolysis of the Bi–C bond upon irradiation; , (3) radical ring-closing forming Bi(III)–I 2 ; and (4) recovery of the Bi(I) species through two-electron reduction.…”