Mechanistic insights for the photoredox organocatalytic fluorination of aliphatic carbons by anthraquinone using time-resolved and DFT studies

• Main Authors: Kee, J. W., Shao, H., Kee, C. W., Lu, Yunpeng, Soo, Han Sen, Tan, Choon Hong
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2018
• Subjects: Photoredox Catalysis; C-H Fluorination; DRNTU::Science::Chemistry
• Online Access: https://hdl.handle.net/10356/87664; http://hdl.handle.net/10220/47035
• Institution: Nanyang Technological University

Chemoselective photoredox fluorination is an appealing approach to access fluorinated fine chemicals such as active pharmaceutical ingredients, but most of the known procedures currently lack time-resolved mechanistic insights. We use nanosecond transient absorption spectroscopy and density functional theory (DFT) calculations to elucidate the elementary steps after irradiation in a photocatalytic fluorination procedure that we reported previously. Time-resolved optical spectroscopy suggests that direct reaction only occurs between the photoexcited anthraquinone (AQN) and Selectfluor®. We have observed spectroscopic evidence of a novel transient AQN–Selectfluor® species for the first time. Further studies by DFT calculations suggest that the AQN–Selectfluor® triplet exciplex formed by photoirradiation is responsible for initiating and sustaining the fluorination reaction.