Cagan, David A. and Bím, Daniel and Silva, Breno and Kazmierczak, Nathanael P. and McNicholas, Brendon J. and Hadt, Ryan G. (2022) Elucidating the Mechanism of Excited-State Bond Homolysis in Nickel–Bipyridine Photoredox Catalysts. Journal of the American Chemical Society, 144 (14). pp. 6516-6531. ISSN 0002-7863. doi:10.1021/jacs.2c01356. https://resolver.caltech.edu/CaltechAUTHORS:20220406-18315469
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Abstract
Ni 2,2′–bipyridine (bpy) complexes are commonly employed photoredox catalysts of bond-forming reactions in organic chemistry. However, the mechanisms by which they operate are still under investigation. One potential mode of catalysis is via entry into Ni(I)/Ni(III) cycles, which can be made possible by light-induced, excited-state Ni(II)–C bond homolysis. Here, we report experimental and computational analyses of a library of Ni(II)–bpy aryl halide complexes, Ni(^Rbpy)(^(R′)Ph)Cl (R = MeO, t-Bu, H, MeOOC; R′ = CH₃, H, OMe, F, CF₃), to illuminate the mechanism of excited-state bond homolysis. At given excitation wavelengths, photochemical homolysis rate constants span 2 orders of magnitude across these structures and correlate linearly with Hammett parameters of both bpy and aryl ligands, reflecting structural control over key metal-to-ligand charge-transfer (MLCT) and ligand-to-metal charge-transfer (LMCT) excited-state potential energy surfaces (PESs). Temperature- and wavelength-dependent investigations reveal moderate excited-state barriers (ΔH^‡ ∼ 4 kcal mol⁻¹) and a minimum energy excitation threshold (∼55 kcal mol⁻¹, 525 nm), respectively. Correlations to electronic structure calculations further support a mechanism in which repulsive triplet excited-state PESs featuring a critical aryl-to-Ni LMCT lead to bond rupture. Structural control over excited-state PESs provides a rational approach to utilize photonic energy and leverage excited-state bond homolysis processes in synthetic chemistry.
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| Additional Information: | © 2022 American Chemical Society. Received: February 3, 2022; Published: March 30, 2022. D.A.C. is a National Science Foundation Graduate Research Fellow (DGE-1745301) and is supported by a National Academies of Science, Engineering, and Medicine Ford Foundation Predoctoral Fellowship. B.S. acknowledges funding through a Southern California Edison WAVE fellowship at Caltech. N.P.K. acknowledges support from the Hertz Fellowship and from the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1745301. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 883987 (D.B.). Support has been provided by the National Institutes of Health (National Institute of General Medical Sciences, R35-GM142595). The authors also acknowledge M. K. Takase in the Beckman Institute X-ray crystallography facility. The computations presented here were conducted in the Resnick High Performance Computing Center, a facility supported by Resnick Sustainability Institute at the California Institute of Technology. The authors declare no competing financial interest. | ||||||||||||||||
| Group: | Resnick Sustainability Institute | ||||||||||||||||
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| Subject Keywords: | Photodissociation, Kinetic parameters, Metal to ligand charge transfer, Ligands, Quantum mechanics | ||||||||||||||||
| Issue or Number: | 14 | ||||||||||||||||
| DOI: | 10.1021/jacs.2c01356 | ||||||||||||||||
| Record Number: | CaltechAUTHORS:20220406-18315469 | ||||||||||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20220406-18315469 | ||||||||||||||||
| Official Citation: | Elucidating the Mechanism of Excited-State Bond Homolysis in Nickel–Bipyridine Photoredox Catalysts. David A. Cagan, Daniel Bím, Breno Silva, Nathanael P. Kazmierczak, Brendon J. McNicholas, and Ryan G. Hadt. Journal of the American Chemical Society 2022 144 (14), 6516-6531; DOI: 10.1021/jacs.2c01356 | ||||||||||||||||
| Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | ||||||||||||||||
| ID Code: | 114168 | ||||||||||||||||
| Collection: | CaltechAUTHORS | ||||||||||||||||
| Deposited By: | George Porter | ||||||||||||||||
| Deposited On: | 06 Apr 2022 10:48 | ||||||||||||||||
| Last Modified: | 24 Mar 2023 19:30 |
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- Elucidating the Mechanism of Excited-State Bond Homolysis in Nickel–Bipyridine Photoredox Catalysts. (deposited 06 Apr 2022 10:48) [Currently Displayed]
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- Cagan, David A. and Bím, Daniel and Silva, Breno and Kazmierczak, Nathanael P. and McNicholas, Brendon J. and Hadt, Ryan G. Elucidating the Mechanism of Excited-State Bond Homolysis in Nickel–Bipyridine Photoredox Catalysts. (deposited 06 Apr 2022 10:48) [Currently Displayed]
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