LNiII(Ar)X (L = bipyridine-type ligand; X = Br and Cl) complexes are fundamental intermediates in photoredox-Ni catalysis for the activation of Csp3–H bonds in Csp3–Csp2 cross-coupling reactions. Their interaction with a light-excited Ir-photocatalyst is assumed to promote the Ni-complex to an excited state from which the Ni–X bond homolysis event occurs. Debate is open on this interaction occurring via single electron transfer (SET) or via energy transfer (EnT), which is the indirect excitation of the Ni-complex by the Ir-photocatalyst. Aiming at addressing this question, we report an electronic structure analysis of these complexes and their 1e– oxidized form using multireference electronic structure methods, which were needed because of the highly multiconfigurational nature of some of the species involved in these reactions. We identified the excited states of LNiII(Ar)X relevant to Ni–X homolysis within the energy range of the irradiating light source, and we propose that they are accessible via triplet Dexter EnT. This is a spin-conserved process with simultaneous exchange of ground- and excited-state electrons between the light-excited Ir-photocatalyst and the Ni-complex. Conversely, SET from LNiII(Ar)X to the Ir-photocatalyst followed by light excitation of the resulting [LNiIII(Ar)X]+ complex is unlikely, as no excited state corresponding to Ni–X dissociation was found in the energy range consistent with the irradiating light source.
|Original language||English (US)|
|Number of pages||10|
|State||Published - Oct 17 2022|
Bibliographical noteKAUST Repository Item: Exported on 2022-10-19
Acknowledged KAUST grant number(s): 4025, 4384
Acknowledgements: B.M. and L.C. acknowledge King Abdullah University of Science and Technology (KAUST) for support and the KAUST Supercomputing Laboratory for providing computational resources of the supercomputer Shaheen II. T.R.S., G.D.S., and L.G. acknowledge the Inorganometallic Catalysis Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under award DE-SC0012702. The authors also gratefully acknowledge the University of Chicago Research Computing Center (RCC), which provided computational resources for this project. T.R.S. acknowledges that this material is also based upon work supported by the National Science Foundation Graduate Research Fellowship Program under grant no. DGE 1746045. L.C. and B.M. acknowledge support from KAUST within the Competitive Research Grant program, under grants no. 4025 and 4384.
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