Positive shift in corrole redox potentials leveraged by modest β-CF₃-substitution helps achieve efficient photocatalytic C–H bond functionalization by group 13 complexes

Abstract

Tris- and tetrakis-β-trifluoromethylated gallium (3CF3-Ga, 4CF3-Ga) and aluminum (3CF3-Al, 4CF3-Al) corrole systems were synthesized by a facile “one-pot” approach and studied in the context of photocatalytic C–H bond activation.

“Hetero‐Multifunctionalization” of Gallium Corroles: Facile Synthesis, Phosphorescence, Redox Tuning, and Photooxidative Catalytic Improvement

“…In the structure, the tetra N‐pyrrolyl pocket containing the central metal reveals [Ga−N] bond lengths ranging from 1.920 to 1.956 Å; these are considered normal Ga−N bond‐length values in comparison to previous reports . One pyridine was observed as the axial ligand coordinating to the Ga with Ga−N bond length of 2.033 Å, close to that observed in other gallium corrole complexes reported before . Unlike trifluoromethylation which most likely induces evident planar distortion as reported before by us, the macrocyclic distortion based on measurements of dihedral angles suggested no evident planar distortion exists upon octa‐bromination of the macrocycle.…”

“…While the 8Br−Ga compound has been reported before, its X‐ray study is now included for the first time (Figure ). In the structure, the tetra N‐pyrrolyl pocket containing the central metal reveals [Ga−N] bond lengths ranging from 1.920 to 1.956 Å; these are considered normal Ga−N bond‐length values in comparison to previous reports . One pyridine was observed as the axial ligand coordinating to the Ga with Ga−N bond length of 2.033 Å, close to that observed in other gallium corrole complexes reported before .…”

“…The observation of how bromination changes the photophysical properties encouraged us to seek quantitative data as acquired from electrochemistry. We found that certain substituents may exert a profound influence on the basic electronic redox potentials such as −CF 3 substitution in gallium corroles that was recently found to be dramatic; compared to non‐substituted species (tpfc)Ga , the tris‐ and tetra‐CF 3 substituted species 3CF 3 −Ga and 4CF 3 −Ga displayed positive shifts of 400 and 440 mV of the 1 st oxidation potential, respectively (the 1 st oxidation potential of 0.37 V for (tpfc)Ga was recorded) . It is of great interest to probe the effect from further bromination on redox properties; Herein, additional CV (cyclic voltammetry) experiments (Figure , Table ) were conducted to help elucidate the electronic effects of tetra‐bromination as well as assessing HOMO‐LUMO energy levels.…”

“…As shown in Figure , a typical Soret band is around 430 nm and several Q bands were observed; all data are provided in Table . Our previous work showed that β‐trifluoromethylation induced red shifts in terms of absorption and emission spectra. Compared to the non‐substituted complex (tpfc)Ga , the tris/tetra‐CF 3 substituted complex 3CF 3 −Ga and 4CF 3 −Ga exhibited small red shifts of 3 and 6 nm in the Soret band and more evident red shifts of 18 and 30 nm in the Q bands.…”

“…In order to prepare gallium corroles that contain two sets of substituents, in which both sets bear multiple substituents, we considered bromination of a well defined multi‐substituted trifluoromethylated corrole system. In this study, we initiated our work from the β‐unsubstituted tpfc gallium framework and then substituted the −CF 3 groups onto β positions and isolated these species . Then, we were able to impart bromination using Br 2 without interfering with the already‐attached −CF 3 groups.…”