Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

• Published in: Journal of the American Chemical Society 2021-09, Vol.143 (38), p.15661-15673
• Main Authors: Aydogan, Akin, Bangle, Rachel E, Cadranel, Alejandro, Turlington, Michael D, Conroy, Daniel T, Cauët, Emilie, Singleton, Michael L, Meyer, Gerald J, Sampaio, Renato N, Elias, Benjamin, Troian-Gautier, Ludovic
• Format: Article
• Language: English
• Subjects: Beverages; Charge transfer; Dehalogenation; Excited states; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; Photosensitization
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.1c06081

Efficient excited-state electron transfer between an iron­(III) photosensitizer and organic electron donors was realized with green light irradiation. This advance was enabled by the use of the previously reported iron photosensitizer, [Fe­(phtmeimb)2]+ (phtmeimb = {phenyl­[tris­(3-methyl-imidazolin-2-ylidene)]­borate}, that exhibited long-lived and luminescent ligand-to-metal charge-transfer (LMCT) excited states. A benchmark dehalogenation reaction was investigated with yields that exceed 90% and an enhanced stability relative to the prototypical photosensitizer [Ru­(bpy)3]2+. The initial catalytic step is electron transfer from an amine to the photoexcited iron sensitizer, which is shown to occur with a large cage-escape yield. For LMCT excited states, this reductive electron transfer is vectorial and may be a general advantage of Fe­(III) photosensitizers. In-depth time-resolved spectroscopic methods, including transient absorption characterization from the ultraviolet to the infrared regions, provided a quantitative description of the catalytic mechanism with associated rate constants and yields.