Visible-Light Photocatalysis of C(sp³ )-H Fluorination by the Uranyl Ion: Mechanistic Insights

The uranyl dication shows photocatalytic activity towards C(sp³ )-H bonds of aliphatic compounds, but not towards those of alkylbenzenes or cyclic ketones. Theoretical insights into the corresponding mechanisms are still limited. Multi-configurational ab initio calculations including relativistic effects reveal the inherent electron-transfer mechanism for the uranyl catalyzed C-H fluorination under blue light. Along the reaction path of the triplet state it was found that the hydrogen atom abstraction triggered by the electron-rich oxygen of the uranyl moiety is the rate-limiting step. The subsequent steps, that is, N-F and O-H bond breakage in a manner of concerted asynchronicity, generation of the targeted fluorinated product, and recovery of the photocatalyst are nearly barrierless. Moreover the single electron transfer between the reactive substrates plays a fundamental role during the whole photocatalytic cycle.