Ion-Pair Reorganization Regulates Reactivity in Photoredox Catalysts

Justin Earley, Anna Zieleniewska, Hunter Ripberger, Nick Shin, Megan Lazorski, Zachary Mast, Hannah Sayre, James McCusker, Greg Scholes, Robert Knowles, Obadiah Reid, Garry Rumbles

Research output: Contribution to journalArticlepeer-review

27 Scopus Citations

Abstract

Cyclometalated and polypyridyl complexes of d6 metals are promising photoredox catalysts, using light to drive reactions with high kinetic or thermodynamic barriers via the generation of reactive radical intermediates. However, while tuning of their redox potentials, absorption energy, excited-state lifetime and quantum yield are well-known criteria for modifying activity, other factors could be important. Here we show that dynamic ion-pair reorganization controls the reactivity of a photoredox catalyst, [Ir[dF(CF3)ppy]2(dtbpy)]X. Time-resolved dielectric-loss experiments show how counter-ion identity influences excited-state charge distribution, evincing large differences in both the ground- and excited-state dipole moment depending on whether X is a small associating anion (PF6) that forms a contact-ion pair versus a large one that either dissociates or forms a solvent-separated pair (BArF4). These differences correlate with the reactivity of the photocatalyst toward both reductive and oxidative electron transfer, amounting to a 4-fold change in selectivity toward oxidation versus reduction. These results suggest that ion pairing could be an underappreciated factor that modulates reactivity in ionic photoredox catalysts. [Figure not available: see fulltext.].

Original languageAmerican English
Pages (from-to)746-753
Number of pages8
JournalNature Chemistry
Volume14
Issue number7
DOIs
StatePublished - Jul 2022

Bibliographical note

Publisher Copyright:
© 2022, The Author(s), under exclusive licence to Springer Nature Limited.

NREL Publication Number

  • NREL/JA-5900-80913

Keywords

  • catalysis
  • dipole
  • excited-state
  • ion pairing
  • Iridium
  • permittivity
  • photoredox
  • polarizability

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