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Multireference Description of Nickel-Aryl Homolytic Bond Dissociation Processes in Photoredox Catalysis

Cagan, David A. and Stroscio, Gautam D. and Cusumano, Alexander Q. and Hadt, Ryan G. (2020) Multireference Description of Nickel-Aryl Homolytic Bond Dissociation Processes in Photoredox Catalysis. Journal of Physical Chemistry A . ISSN 1089-5639. (In Press) https://resolver.caltech.edu/CaltechAUTHORS:20200925-135425759

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Abstract

Multireference electronic structure calculations consistent with known experimental data have elucidated a novel mechanism for photo-triggered Ni(II)–C homolytic bond dissociation in Ni 2,2′-bipyridine (bpy) photoredox catalysts. Previously, a thermally assisted dissociation from the lowest energy triplet ligand field excited state was proposed and supported by density functional theory (DFT) calculations that reveal a barrier of ∼30 kcal mol⁻¹. In contrast, multireference ab initio calculations suggest that this process is disfavored, with barrier heights of ∼70 kcal mol⁻¹, and highlight important ligand noninnocent and multiconfigurational contributions to excited state relaxation and bond dissociation processes that are not captured with DFT. In the multireference description, photo-triggered Ni(II)–C homolytic bond dissociation occurs via initial population of a singlet Ni(II)-to-bpy metal-to-ligand charge transfer (¹MLCT) excited state, followed by intersystem crossing and aryl-to-Ni(III) charge transfer, overall a formal two-electron transfer process driven by a single photon. This results in repulsive triplet excited states from which spontaneous homolytic bond dissociation can occur, effectively competing with relaxation to the lowest energy nondissociative triplet Ni(II) ligand field excited state. These findings guide important electronic structure considerations for the experimental and computational elucidation of the mechanisms of ground and excited state cross-coupling catalysis mediated by Ni heteroaromatic complexes.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://dx.doi.org/10.1021/acs.jpcaDOIArticle
https://pubs.acs.org/doi/10.1021/acs.jpca.0c08646PublisherArticle
https://doi.org/10.26434/chemrxiv.12990830.v1DOIDiscussion Paper
ORCID:
AuthorORCID
Stroscio, Gautam D.0000-0002-0827-1062
Cusumano, Alexander Q.0000-0002-2914-2008
Hadt, Ryan G.0000-0001-6026-1358
Additional Information:© 2020 American Chemical Society. Received: September 22, 2020; Revised: November 9, 2020; Publication Date: November 23, 2020. 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. Financial support from Caltech and the Dow Next Generation Educator Fund is gratefully acknowledged. Author Contributions: Co-first authors. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1745301
Ford FoundationUNSPECIFIED
CaltechUNSPECIFIED
Dow Next Generation Educator FundUNSPECIFIED
Subject Keywords:Charge Transfer; Excited States; Nickel; Cross-Coupling Reactions; Photophysics; Photocatalysis
Record Number:CaltechAUTHORS:20200925-135425759
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200925-135425759
Official Citation:Multireference Description of Nickel–Aryl Homolytic Bond Dissociation Processes in Photoredox Catalysis. David A. Cagan, Gautam D. Stroscio, Alexander Q. Cusumano, and Ryan G. Hadt. The Journal of Physical Chemistry A. Article ASAP; DOI: 10.1021/acs.jpca.0c08646
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105568
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:25 Sep 2020 22:25
Last Modified:23 Nov 2020 19:34

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