Zwitterionic Acridinium Amidate: A Nitrogen-Centered Radical Catalyst for Photoinduced Direct Hydrogen Atom Transfer

The development of small organic molecules that can convert light energy into chemical energy to directly promote molecular transformation is of fundamental importance in chemical science. Herein, we report a zwitterionic acridinium amidate as a catalyst for the direct functionalization of aliphatic C-H bonds. This organic zwitterion absorbs visible light to generate the corresponding amidyl radical in the form of excited-state triplet diradical with prominent reactivity for hydrogen atom transfer to facilitate C-H alkylation with a high turnover number. The experimental and theoretical investigations revealed that the noncovalent interactions between the anionic amidate nitrogen and a pertinent hydrogen-bond donor, such as hexafluoroisopropanol, are crucial for ensuring the efficient generation of catalytically active species, thereby fully eliciting the distinct reactivity of the acridinium amidate as a photoinduced direct hydrogen atom transfer catalyst. Despite the long and rich history of photoinduced direct hydrogen atom transfer (d-HAT) catalysis, the primary structures of existing catalysts rely on molecular entities containing oxo groups, particularly with aromatic ketones and inorganic polyoxometalates. Here, we disclose zwitterionic acridinium amidate as a photoreactive nitrogen-centered radical precursors, which exhibit prominent reactivity to cleave aliphatic C-H bonds. image