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Photocatalytic activation of alkyl chlorides by assembly-promoted single electron transfer in microheterogeneous solutions

Abstract

Photoredox catalysis has developed into a powerful tool for the synthesis of organic compounds with diverse structures. However, stable carbon–chloride bonds remain beyond the energetic limits of the outer-sphere photoreductive activation. Here, we demonstrate that the organization of the reacting species in microstructured, aqueous solutions allows generation of carbon-centred radicals from non-activated alkyl chlorides in the presence of double bonds via assembly-promoted single electron transfer. Photocatalytic systems consisting of a surfactant, organic substrates and additives have been designed, characterized and applied for radical dechlorination, addition and cyclization reactions. Cheap and commercially available blue light-emitting diodes are used as the irradiation source for the transformations. Mechanistic studies indicate the accumulation of the energy of two visible light photons in one catalytic cycle.

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Fig. 1: Light-driven strategies for activation of C–Cl bonds.
Fig. 2: Spectroscopic investigation on stability of [Ir(dtbby)·(ppy)2] species.
Fig. 3: The synthetic scope of the reductive dehalogenation.
Fig. 4: Developing a method for photoreductive C–C coupling.
Fig. 5: Inter- and intramolecular photoreductive C–C bond-forming reactions.
Fig. 6: Mechanistic investigations.
Fig. 7: Proposed mechanism for the dehalogenation of alkyl chlorides and addition to electron-deficient olefins.

Data availability

Data relating to the materials and methods, optimization studies, experimental procedures, mechanistic studies, DLS measurements and NMR spectra are available in the Supplementary Information. All other data are available from the authors upon reasonable request.

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Acknowledgements

We gratefully acknowledge funding from the German Research Foundation (DFG, GRK 1626, Chemical Photocatalysis and KO 1537/18-1) and the Ministry of Science and Higher Education of Poland (M.G., Mobility Plus, 1640/MOB/V/2017/0). We thank S. Crespi for his help with preparing the graphics.

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B.K. guided the research. B.K. and M.G. conceived and designed the project. M.G. performed most of the experiments and wrote the manuscript, with input from others. R.N. expanded the scope of radical cyclization reactions. S.W. carried out part of the optimization experiments. D.T. and W.K. envisaged and interpreted the effects of different surfactants, designed and analysed the DLS experiments. All authors discussed the results and commented on the manuscript.

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Correspondence to Werner Kunz or Burkhard König.

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Supplementary Information

Supplementary Methods, Tables 1–7, Figs. 1–10 and references.

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Giedyk, M., Narobe, R., Weiß, S. et al. Photocatalytic activation of alkyl chlorides by assembly-promoted single electron transfer in microheterogeneous solutions. Nat Catal 3, 40–47 (2020). https://doi.org/10.1038/s41929-019-0369-5

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