Enantioselective catalytic processes are promoted by chiral catalysts that can execute a specific mode of catalytic reactivity, channeling the chemical reaction through a certain mechanistic pathway. Here, we show how by simply using visible light we can divert the established ionic reactivity of a chiral allyl–iridium(iii) complex to switch on completely new catalytic functions, enabling mechanistically unrelated radical-based enantioselective pathways. Photoexcitation provides the chiral organometallic intermediate with the ability to activate substrates via an electron-transfer manifold. This redox event unlocks an otherwise inaccessible cross-coupling mechanism, since the resulting iridium(ii) centre can intercept the generated radicals and undergo a reductive elimination to forge a stereogenic centre with high stereoselectivity. This photochemical strategy enables difficult-to-realize enantioselective alkyl–alkyl cross-coupling reactions between allylic alcohols and readily available radical precursors, which are not achievable under thermal activation.
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The data that support the findings of this study are available in the Supplementary Information (experimental procedures and characterization data). Crystallographic data for the structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers CCDC 2021458 (4g) and 2021459 (4h). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/.
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This work is dedicated to the memory of Professor Kilian Muñiz. Financial support was provided by Agencia Estatal de Investigación (PID2019-106278GB-I00 and CTQ2016-75520-P), the AGAUR (Grant 2017 SGR 981) and the European Research Council (ERC-2015-CoG 681840-CATA-LUX). G.E.M.C. thanks the EU for a Horizon 2020 Marie Skłodowska-Curie Fellowship (H2020-MSCA-IF-2017, 795793). D.M. thanks H2020-MSCA-ITN-2016 (722591–PHOTOTRAIN) for a predoctoral fellowship. We thank A. Llobet and J. Holub for assistance with differential pulse voltammetry and E. E. Adán for help with X-ray crystallographic analysis.
The authors declare no competing interests.
Peer review information Nature Chemistry thanks the anonymous reviewer(s) for their contribution to the peer review of this work.
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Crisenza, G.E.M., Faraone, A., Gandolfo, E. et al. Catalytic asymmetric C–C cross-couplings enabled by photoexcitation. Nat. Chem. 13, 575–580 (2021). https://doi.org/10.1038/s41557-021-00683-5