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Pushing the Limits of Organometallic Redox Chemistry with an Isolable Mn(−I) Dianion

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Neugebauer,  Hagen
Research Department Neese, Max-Planck-Institut für Kohlenforschung, Max Planck Society;
Mulliken Center for Theoretical Chemistry, Clausius-Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn;

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Citation

Karagiannis, A., Neugebauer, H., Lalancette, R. A., Grimme, S., Hansen, A., & Prokopchuk, D. E. (2024). Pushing the Limits of Organometallic Redox Chemistry with an Isolable Mn(−I) Dianion. Journal of the American Chemical Society, 146(28), 19279-19285. doi:10.1021/jacs.4c04561.


Cite as: https://hdl.handle.net/21.11116/0000-000F-91DB-6
Abstract
We report an incredibly reducing and redox-active Mn–I dianion, [Mn(CO)3(Ph2B(tBuNHC)2)]2– (NHC = N-heterocyclic carbene), furnished via 2e reduction of the parent 16e MnI complex with Na0 or K0. Cyclic voltammograms show a Mn0/–I redox couple at −3.13 V vs Fc+/0 in tetrahydrofuran (THF), −3.06 V in 1,2-dimethoxyethane, and −2.85 V in acetonitrile. The diamagnetic Mn–I dianion is stable in solution and solid-state at room temperature, tolerating a wide range of countercations ([M(2.2.2)crypt]+, [M(18-crown-6)]+, [nBu4N]+; M = Na, K). Countercation identity does not significantly alter 13C NMR spectral signatures with [nBu4N]+ and Na+, suggesting minimal ion pairing in solution. IR spectroscopy reveals a significant decrease in CO stretching frequencies from MnI to Mn–I (ca. 240 cm–1), consistent with a drastic increase in electron density at Mn. State-of-the-art DFT calculations are in excellent agreement with the observed IR spectral data. Moreover, the Mn–I dianion behaves as a chemical reductant, smoothly releasing 1e or 2e to regenerate the oxidized Mn0 or MnI species in solution. The reducing potential of [Mn(CO)3(Ph2B(tBuNHC)2)]2- surpasses the naphthalenide anion in THF (−3.09 V) and represents one of the strongest isolable chemical redox agents.