Ultrafast Spectroscopy of [Mn(CO)3] Complexes: Tuning the Kinetics of Light-Driven CO Release and Solvent Binding

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Issue Date
2020-01-28Author
Henke, Wade C.
Otolski, Christopher J.
Moore, William N. G.
Elles, Christopher G.
Blakemore, James D.
Publisher
American Chemical Society
Type
Article
Article Version
Scholarly/refereed, author accepted manuscript
Rights
Copyright © 2020 American Chemical Society
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Manganese tricarbonyl complexes are promising catalysts for CO2 reduction, but complexes in this family are often photo-sensitive and decompose rapidly upon exposure to visible light. In this report, synthetic and photochemical studies probe the initial steps of light-driven speciation for Mn(CO)3(Rbpy)Br complexes bearing a range of 4,4′-disubstituted-2,2′-bipyridyl ligands (Rbpy, R = tBu, H, CF3, NO2). Transient absorption spectroscopy measurements for the Mn(CO)3(Rbpy)Br coordination compounds with R = tBu, H, and CF3 in acetonitrile reveal ultrafast loss of a CO ligand on the femtosecond timescale, followed by solvent coordination on the picosecond timescale. The Mn(CO)3(NO2bpy)Br complex is unique among the four compounds in having a longer-lived excited state that does not undergo CO release or the subsequent solvent coordination. The kinetics of photolysis and solvent coordination for the light-sensitive complexes depend on the electronic properties of the di-substituted bipyridyl ligand. The results implicate roles for both metal-to-ligand charge transfer (MLCT) and dissociative ligand field (dd) excited states in the ultrafast photochemistry. Taken together, the findings suggest that more robust catalysts could be prepared with appropriately designed complexes that avoid crossing between the excited states that drive photochemical CO loss.
Description
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.9b02758.
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Citation
Henke, W. C., Otolski, C. J., Moore, W., Elles, C. G., & Blakemore, J. D. (2020). Ultrafast Spectroscopy of [Mn(CO)3] Complexes: Tuning the Kinetics of Light-Driven CO Release and Solvent Binding. Inorganic chemistry, 59(4), 2178–2187. https://doi.org/10.1021/acs.inorgchem.9b02758
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