Photostable Polynuclear Ruthenium(II) Photosensitizers Competent for Dehalogenation Photoredox Catalysis at 590 nm
Simon Cerfontaine, Sara A. M. Wehlin, Benjamin Elias, Ludovic Troian‐Gautier
Abstract
Higher nuclearity photosensitizers produced dehalogenation yields greater than 90% in the reported [Ru(bpy)3]2+-mediated dehalogenation of 4-bromobenzyl-2-chloro-2-phenylacetate to 4-bromobenzyl-2-phenylacetate with orange light in 7 h, whereas after 72 h yields of 49% were obtained with [Ru(bpy)3]2+. Dinuclear (D1), trinuclear (T1), and quadrinuclear (Q1) ruthenium(II) 2,2′-bipyridine based photosensitizers were synthesized, characterized, and investigated for their photoreactivity. Three main factors were shown to lead to increased yields (i) the red-shifted absorbance of polynuclear photosensitizers, (ii) the more favorable driving force for electron transfer, characterized by more positive E1/2(Ru2+*/+), and (iii) the smaller population of the 3MC state (<0.5% for D1, T1 and Q1 vs 48% for [Ru(bpy)3]2+ at room temperature). Collectively, these results highlight the potential advantages of using polynuclear photosensitizers in phototriggered redox catalysis reactions.