Carbon nitrides as a versatile platform for net-oxidative and net-neutral photoredox catalysis Alexey Galushchinskiy, Aleksandr Savateev, Markus Antonietti Max Planck Institute of Colloids and Interfaces, Germany In the last years, photoredox catalysis has become a powerful tool for synthetic chemists due to its versatility and broad variety of supported single-electron transfer reactions, which range from late-stage introduction of the isotope labels to complex transformations of organic compounds. 1 One of the most notable classes of currently available heterogenous photocatalysts are carbon nitrides, which show similar activity to Ru- and Ir-based photocatalysts as well as enable unique transformations, and can be easily isolated from reaction mixture and then re-used multiple times. 2 For instance, carbon nirides allow for various oxygenation reactions to proceed using only molecular oxygen as a terminal oxidant. This was demonstrated by cleavage of oximes back to parent carbonyl compounds by potassium poly(heptazine imide) (K-PHI) photocatalyst, which has certain synthetic utility for introduction of keto group via nitrosation products and served as a model reaction to further investigate the photophysics of singlet oxygen photocatalytic generation (Figure 1a). 3 Another example is conversion of 1,3-oxazolidin-2-ones to corresponding 1,3-oxazolidine-2,4-diones using mesoporous graphitic carbon nitride (mpg-CN) (Figure 1b). This transformation is otherwise challenging due to high oxidation potentials of the substrates, but basic character of mpg-CN allow it to proceed via proton-coupled electron transfer, which was corroborated by experimental data and DFT calculations. This process opens synthetic pathway to moieties that are useful in medicinal and agricultural chemistry. 4 In our attempt to create a versatile carbon nitride photocatalyst, we’ve developed a series of new multi-phase materials called Rho-CNs, which consist primarily of poly(triazine imide) (Figure 1c). Rho-CNs are prepared in high yield in two steps fashion via a pre-polymer of cyanamide and a small amount of potassium rhodizonate salt, yielding photocatalysts capable of oxidation of benzylamine with good reaction rates at 625 nm irradiation. 5 These materials were also utilized in dual nickel photoredox C-N cross-coupling reactions, and demonstrated chromoselective behavior in oxidation of S -acetylthiophenol 6 giving either benzenesulfonyl chloride or diphenyl disulfide as a product depending on whether 465 nm or 535 nm light source was used, respectively.
Figure 1. Net-oxidative and net-neutral photocatalytic transformations provided by carbon nitrides. a) Oxygenative photocatalytic cleavage of oximes using K-PHI catalyst. b) Photocatalytic oxidation of oxazolidinones to corresponding 2,4-diones using mpg- CN catalyst. c) Preparation and summary of photocatalytic activity for multi-phase carbon nitride species Rho-CN. References 1. R. C. McAtee, E. J. McClain, C. R. J. Stephenson, Trends Chem. 2019 , 1, 111–125 2. A. Savateev, B. Kurpil, A. Mishchenko, G. Zhang, M. Antonietti, Chem. Sci. 2018 , 9, 3584–3591 3. A. Galushchinskiy, K. ten Brummelhuis, M. Antonietti, A. Savateev. ChemPhotoChem , 2021 , 5 (11), 1020–1025 4. A. Galushchinskiy, Y. Zou, J. Odutola, P. Nika ević, J.-W. Shi, N. Tkachenko, N. López, P. Farràs, O. Savateev, Angew. Chem. Int. Ed. (in submission). A. Galushchinskiy, C. Pulignani, E. Reisner, O. Savateev, Solar RRL (in submission).Y. Markushyna, C. M. Schüßlbauer, T. Ullrich, D. M. Guldi, M. Antonie ti, A. Savateev, Angew. Chem. Int. Ed., 2021 ,60, 20543.
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