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

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

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2021

0002-7863

Efficient excited-state electron transfer between aniron(III) photosensitizer and organic electron donors was realized withgreen light irradiation. This advance was enabled by the use of thepreviously reported iron photosensitizer, [Fe(phtmeimb)2]+ (phtmeimb= {phenyl[tris(3-methyl-imidazolin-2-ylidene)]borate}, that exhibitedlong-lived and luminescent ligand-to-metal charge-transfer (LMCT)excited states. A benchmark dehalogenation reaction was investigatedwith yields that exceed 90% and an enhanced stability relative to theprototypical photosensitizer [Ru(bpy)3]2+. The initial catalytic step iselectron transfer from an amine to the photoexcited iron sensitizer, whichis shown to occur with a large cage-escape yield. For LMCT excitedstates, this reductive electron transfer is vectorial and may be a generaladvantage 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.