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Proton Coupled Electron Transfer from the Excited State of a Ruthenium(II) Pyridylimidazole Complex

Pannwitz, Andrea and Wenger, Oliver S.. (2016) Proton Coupled Electron Transfer from the Excited State of a Ruthenium(II) Pyridylimidazole Complex. Physical Chemistry Chemical Physics, 18 (16). pp. 11374-11382.

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Abstract

Proton coupled electron transfer (PCET) from the excited state of [Ru(bpy)2pyimH]2+ (bpy = 2,2′-bipyridine; pyimH = 2-(2′-pyridyl)imidazole) to N-methyl-4,4′-bipyridinium (monoquat, MQ+) was studied. While this complex has been investigated previously, our study is the first to show that the formal bond dissociation free energy (BDFE) of the imidazole-N–H bond decreases from (91 ± 1) kcal mol−1 in the electronic ground state to (43 ± 5) kcal mol−1 in the lowest-energetic 3MLCT excited state. This makes the [Ru(bpy)2pyimH]2+ complex a very strong (formal) hydrogen atom donor even when compared to metal hydride complexes, and this is interesting for light-driven (formal) hydrogen atom transfer (HAT) reactions with a variety of different substrates. Mechanistically, formal HAT between 3MLCT excited [Ru(bpy)2pyimH]2+ and monoquat in buffered 1 : 1 (v : v) CH3CN/H2O was found to occur via a sequence of reaction steps involving electron transfer from Ru(II) to MQ+ coupled to release of the N–H proton to buffer base, followed by protonation of reduced MQ+ by buffer acid. Our study is relevant in the larger contexts of photoredox catalysis and light-to-chemical energy conversion.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Wenger)
UniBasel Contributors:Wenger, Oliver and Pannwitz, Andrea
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:Royal Society of Chemistry
ISSN:1463-9076
e-ISSN:1463-9084
Note:Publication type according to Uni Basel Research Database: Journal article
Language:English
Identification Number:
Last Modified:11 Jan 2017 13:23
Deposited On:11 Jan 2017 13:23

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