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Title: How Radical Are "Radical" Photocatalysts? A Closed-Shell Meisenheimer Complex Is Identified as a Super-Reducing Photoreagent
Super-reducing excited states have the potential to activate strong bonds, leading to unprecedented photoreactivity. Excited states of radical anions, accessed via reduction of a precatalyst followed by light absorption, have been proposed to drive photoredox transformations under super-reducing conditions. Here, we investigate the radical anion of naphthalene monoimide as a photoreductant and find that the radical doublet excited state has a lifetime of 24 ps, which is too short to facilitate photoredox activity. To account for the apparent photoreactivity of the radical anion, we identify an emissive two-electron reduced Meisenheimer complex of naphthalene monoimide, [NMI(H)](-). The singlet excited state of [NMI(H)](-) is a potent reductant (-3.08 V vs Fc/Fc(+)), is long-lived (20 ns), and its emission can be dynamically quenched by chloroarenes to drive a radical photochemistry, establishing that it is this emissive excited state that is competent for reported C-C and C-P coupling reactivity. These results provide a mechanistic basis for photoreactivity at highly reducing potentials via singlet excited state manifolds and lays out a clear path for the development of exceptionally reducing photoreagents derived from electron-rich closed-shell anions.  more » « less
Award ID(s):
1855531
NSF-PAR ID:
10352270
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Journal of the American Chemical Society
Volume:
143
Issue:
35
ISSN:
0002-7863
Page Range / eLocation ID:
14352–14359
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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