Insights into the Role of Graphitic Carbon Nitride as a Photobase in Proton‐Coupled Electron Transfer in (sp<sup>3</sup>)C−H Oxygenation of Oxazolidinones
Alexey Galushchinskiy, Yajun Zou, Jokotadeola Odutola, Pavle Nikačević, Jian‐Wen Shi, Nikolai V. Tkachenko, Núria López, Pau Farràs, Aleksandr Savateev
Abstract
Abstract Graphitic carbon nitride (g‐CN) is a transition metal free semiconductor that mediates a variety of photocatalytic reactions. Although photoinduced electron transfer is often postulated in the mechanism, proton‐coupled electron transfer (PCET) is a more favorable pathway for substrates possessing X−H bonds. Upon excitation of an (sp 2 )N‐rich structure of g‐CN with visible light, it behaves as a photobase—it undergoes reductive quenching accompanied by abstraction of a proton from a substrate. The results of modeling allowed us to identify active sites for PCET—the ‘triangular pockets’ on the edge facets of g‐CN. We employ excited state PCET from the substrate to g‐CN to selectively cleavethe endo ‐(sp 3 )C−H bond in oxazolidine‐2‐ones followed by trapping the radical with O 2 . This reaction affords 1,3‐oxazolidine‐2,4‐diones. Measurement of the apparent p K a value and modeling suggest that g‐CN excited state can cleave X−H bonds that are characterized by bond dissociation free energy (BDFE) ≈100 kcal mol −1 .