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.
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Photoredox‐Mediated Net‐Neutral Radical/Polar Crossover Reactions
Radical/Polar Crossover (RPC) chemistry is a rapidly growing subset of photoredox catalysis that is characterized by transformations featuring both radical and ionic modes of reactivity. Net‐neutral RPC is particularly interesting in that both the single‐electron oxidation and reduction steps occur through interaction with the photocatalyst, thus precluding the need for exogenous oxidants or reductants. As such, these transformations facilitate rapid incorporation of molecular complexity while maintaining mild reaction conditions. This review covers recent advances in photoredox‐mediated net‐neutral RPC synthetic methods, with a particular emphasis on C–C bond‐forming reactions.
more » « less- NSF-PAR ID:
- 10135114
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Israel Journal of Chemistry
- Volume:
- 60
- Issue:
- 3-4
- ISSN:
- 0021-2148
- Page Range / eLocation ID:
- p. 281-293
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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