Semi‐heterogeneous Dual Nickel/Photocatalysis using Carbon Nitrides: Esterification of Carboxylic Acids with Aryl Halides

Abstract

Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/anie.201902785. Scheme 1. Homogeneous versus semi-heterogeneous dual Ni/photocatalysis. Angewandte Chemie Communications Angewandte Chemie Communications 9577 Angew.C hem. Int.E d. 2019, 58,9 575 -9580

General Paradigm in Photoredox Nickel‐Catalyzed Cross‐Coupling Allows for Light‐Free Access to Reactivity

“…The success of aryl esterification is noteworthy given the diminished nucleophilicity of carboxylates relative to other heteroatomic cross‐coupling substrates, as demonstrated by the requirement for super‐stoichiometric amounts of silver salts in a reported Pd‐catalyzed methodology for the esterification of aryl iodides, and a scarcity of examples for the direct cross‐coupling of carboxylic acids with aryl bromides under thermal nickel catalysis. Moreover, reports of this transformation under photochemical conditions unanimously invoke photosensitization pathways that necessitate access to a Ni II excited state as a precondition for reductive elimination, whereas our reactions in the absence of light preclude any possibility of excited‐state formation. These results suggest a Ni I/III pathway as an alternative, and hitherto unexplored, mechanistic strategy for achieving this transformation.…”

“…Our results show that Ni‐catalyzed amination, etherification, and esterification of aryl bromides can all be realized across a wide range of substrates without light under conditions that otherwise bear resemblance to the parent photochemical methodologies. To this end, one may wish to re‐evaluate the growing body of literature that invokes energy transfer as the mechanism for catalysis . As we show here, only a small amount of Ni I can initiate self‐sustained Ni I /Ni III thermal catalysis.…”

Ionic Carbon Nitrides in Solar Hydrogen Production and Organic Synthesis: Exciting Chemistry and Economic Advantages

“…Pieber et al. have coupled Ni‐catalyst with CN‐OA‐m photocatalyst for selective C−O coupling of carboxylic acids and arylhalides (Scheme ) . The idea behind this intriguing combination of the catalysts is to use carbon nitride, with the advantages of heterogeneous approach discussed in the introduction, for reduction of the intermediary Ni(I)‐molecular complex …”

Organic Photocatalysis: Carbon Nitride Semiconductors vs. Molecular Catalysts

“…Another variation of carbon‐oxygen coupling by CN/Ni catalysis was showed by Pieber and co‐authors (Scheme ). Esterification of carboxylic acids with aryl halides was performed under mild conditions . The catalyst system was shown to harvest a broad range of visible‐light spectrum (up to 600 nm), which was shown by in situ FT‐IR analysis of the reaction progress.…”