Mechanistic insights for the photoredox organocatalytic fluorination of aliphatic carbons

by anthraquinone using time-resolved and DFT studies

Kee, J. W.; Shao, H.; Kee, C. W.; Lu, Y.; Soo, H. S.; Tan, C.-H

Catalysis Science & Technology, 2017, 7, 848-857

Abstract: Chemoselective photoredox fluorination is an appealing approach to access fluorinated fine chems. such as active pharmaceutical ingredients, but most of the known procedures currently lack time-resolved mechanistic insights. The authors use nanosecond transient absorption spectroscopy and d. functional theory (DFT) calculations to elucidate the elementary steps after irradiation in a photocatalytic fluorination procedure that the authors reported previously. Time-resolved optical spectroscopy suggests that direct reaction only occurs between the photoexcited anthraquinone (AQN) and Selectfluor. The authors 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.

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