Ion-pair reorganization regulates reactivity in photoredox catalysts

Cyclometalated and polypyridyl complexes of d 6 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-stat...

Full description

Saved in:

Bibliographic Details
Published in:	Nature chemistry Vol. 14; no. 7; pp. 746 - 753
Main Authors:	Earley, J. D., Zieleniewska, A., Ripberger, H. H., Shin, N. Y., Lazorski, M. S., Mast, Z. J., Sayre, H. J., McCusker, J. K., Scholes, G. D., Knowles, R. R., Reid, O. G., Rumbles, G.
Format:	Journal Article
Language:	English
Published:	London Nature Publishing Group UK 01-07-2022 Nature Publishing Group
Subjects:	639/638/263/406/939 639/638/439/890 639/638/440/949 639/638/77/890 Analytical Chemistry Biochemistry Catalysts Charge distribution Chemistry Chemistry and Materials Science Chemistry/Food Science CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS Dipole moments Electron transfer Excitation Inorganic Chemistry INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Intermediates ion pairing Ion pairs Ligands Metals Organic Chemistry OTHER INSTRUMENTATION Oxidation Photocatalysis Photoredox catalysis Physical Chemistry Reactivity Selectivity Solvents Time-resolved dielectric-loss (TRDL) spectroscopy
Online Access:	Get full text
Tags:	Add Tag No Tags, Be the first to tag this record!

Description
Summary:	Cyclometalated and polypyridyl complexes of d 6 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(CF 3 )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 (PF 6 − ) that forms a contact-ion pair versus a large one that either dissociates or forms a solvent-separated pair (BAr F 4 − ). 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. Ion pairing is ubiquitous in low-dielectric-constant solvents, but whether it influences the reactivity of common cationic photoredox catalysts has been unclear. However, it has now been shown that ion pairing is responsible for a 4-fold modulation in reactivity in a prototypical Ir(III) complex and is explained by excited-state ion-pair reorganization.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 SC0019370; AC36-08GO28308 USDOE Office of Science (SC)
ISSN:	1755-4330 1755-4349
DOI:	10.1038/s41557-022-00911-6