Monitoring radical intermediates in photoactivated palladium-catalysed coupling of aryl halides to arenes by an aryl radical assay

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Tyerman, Seb and MacKay, Donald G. and Clark, Kenneth F. and Kennedy, Alan R. and Robertson, Craig M. and Evans, Laura and Edkins, Robert M. and Murphy, John A. (2024) Monitoring radical intermediates in photoactivated palladium-catalysed coupling of aryl halides to arenes by an aryl radical assay. ACS Catalysis. ISSN 2155-5435 (In Press) (https://doi.org/10.1021/acscatal.4c06913)

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Abstract

An aryl radical assay is used to provide information about the formation of aryl radicals from aryl halides in coupling reactions to arenes in the presence of palladium sources and under LED irradiation (λ = 456 nm). The assay uses 2-halo-m-xylenes as substrates. Aryl radical formation is indicated both by a defined product composition and by signature deuterium isotope effects. Comparison with our recently published results for corresponding ground state palladium-catalysed reactions shows three principal differences: (i) in the photoactivated 2 reactions, evidence supports the formation of aryl radical intermediates with all the phosphine ligands tested, in contrast to thermal ground-state chemistry where only specific ligands had encouraged this pathway, while others had promoted a non-radical coupling mechanism; (ii) oxidative addition complexes that are formed from reaction of Pd(0) sources with aryl halides react under photoactivation to form biaryl coupled products through radical intermediates, in contrast to their behaviour under thermal activation - so Ar-Pd bonds are homolysed under LED irradiation; (iii) the photoreactions work well with mild bases like Cs2CO3, while the thermal reactions required KOtBu as base due to the different roles for base under the thermal versus photochemical mechanisms.

ORCID iDs

Tyerman, Seb, MacKay, Donald G., Clark, Kenneth F., Kennedy, Alan R. ORCID logoORCID: https://orcid.org/0000-0003-3652-6015, Robertson, Craig M., Evans, Laura, Edkins, Robert M. ORCID logoORCID: https://orcid.org/0000-0001-6117-5275 and Murphy, John A.;
  • Item type:Article
    ID code:91600
    Dates:
    Date
    Event
    16 December 2024
    Published
    16 December 2024
    Accepted
    Subjects:Science > Chemistry
    Department:Faculty of Science > Pure and Applied Chemistry
    Depositing user: Pure Administrator
    Date deposited:17 Dec 2024 15:07
    Last modified:17 Dec 2024 15:07
    URI:https://strathprints.strath.ac.uk/id/eprint/91600
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