Mechanistic investigation of a visible light mediated dehalogenation/cyclisation reaction using iron(), iridium() and ruthenium() photosensitizers

• Published in: Catalysis science & technology Vol. 11; no. 24; pp. 837 - 851
• Main Authors: Aydogan, Akin, Bangle, Rachel E, De Kreijger, Simon, Dickenson, John C, Singleton, Michael L, Cauët, Emilie, Cadranel, Alejandro, Meyer, Gerald J, Elias, Benjamin, Sampaio, Renato N, Troian-Gautier, Ludovic
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 14.12.2021
• Subjects: Dichloromethane; Infrared spectroscopy; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; Iridium; Iron; Photoluminescence; Reaction mechanisms; Ruthenium; Ruthenium compounds; Solvents; Spectrum analysis; Transition metals
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d1cy01771c

The mechanism of a visible light-driven dehalogenation/cyclization reaction was investigated using ruthenium( ii ), iridium( iii ) and iron( iii ) photosensitizers by means of steady-state photoluminescence, time-resolved infrared spectroscopy, and nanosecond/femtosecond transient absorption spectroscopy. The nature of the photosensitizer was found to influence the product distribution such that the dehalogenated, non-cyclized products were only detected for the iron photosensitizer. Strikingly, with the iron photosensitizer, large catalytic yields required a low dielectric solvent such as dichloromethane, consistent with a previous publication. This low dielectric solvent allowed ultrafast charge-separation to outcompete geminate charge recombination and improved cage escape efficiency. Further, the identification of reaction mechanisms unique to the iron, ruthenium, and iridium photosensitizer represents progress towards the long-sought goal of utilizing earth-abundant, first-row transition metals for emerging energy and environmental applications. The identification of reaction mechanisms unique to the iron, ruthenium, and iridium PS represents progress towards the long-sought goal of utilizing earth-abundant, first-row transition metals for emerging energy and environmental applications.