Stabilizing an exotic dianionic tetrazine bridge in a Ln2 metallocene
Mavragani, Niki; Kitos, Alexandros A; Mansikkamäki, Akseli; Murugesu, Muralee (2024-09-06)
Mavragani, Niki
Kitos, Alexandros A
Mansikkamäki, Akseli
Murugesu, Muralee
Royal society of chemistry
06.09.2024
Mavragani, N., Kitos, A. A., Mansikkamäki, A., & Murugesu, M. (2024). Stabilizing an exotic dianionic tetrazine bridge in a Ln 2 metallocene. Chemical Science, 15(39), 16234–16242. https://doi.org/10.1039/D4SC03734K
https://creativecommons.org/licenses/by-nc/3.0/
© 2024 The Author(s). Published by the Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.
https://creativecommons.org/licenses/by-nc/3.0/
© 2024 The Author(s). Published by the Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.
https://creativecommons.org/licenses/by-nc/3.0/
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:oulu-202409205985
https://urn.fi/URN:NBN:fi:oulu-202409205985
Tiivistelmä
Abstract
The unique electronic nature of the 1,2,4,5-tetrazine or s-tetrazine (tz) ring has sparked tremendous scientific interest over the last few years. Tetrazines have found numerous applications, and their ability to coordinate to metal ions has opened the possibility of exploring their chemistry in both molecular systems and extended networks. The rich redox chemistry of s-tetrazines allows them to exchange electrons and switch between their dihydro (H2tz), neutral (tz), and radical (tz˙−) forms. Previous reports in the literature have observed electrochemically that a second electron can potentially be stored in the tetrazinyl ring and form a dianionic species. However, due to its extremely reactive nature, this has not been isolated before. Herein, the combination of strictly anhydrous and inert conditions, strong reducing agents, non-acidic solvents and most importantly blocking the accessibility of the nitrogen atoms by coordinating them to lanthanide ions allowed for the stabilization of a dianionic tetrazine in a lanthanocene complex. Three dinuclear metallocene complexes are reported, [(Cp*2Ln)2(tz˙−)(THF)2](BPh4) (Ln = Y (1-Y); Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) and [(Cp*2Ln)2(tz2−)(THF)2]·2THF (Ln = Gd (2-Gd), or Y (2-Y)), which utilize the unsubstituted tz as the ligand. In 1-Ln, the tz ligand is reduced to the radical anion (tz˙−), while in 2-Ln, the tz ligand is in the −2 charge state. These complexes are the first structurally and physically characterized complexes bearing the dianion radical of an s-tetrazine. Detailed structural analysis, ab initio calculations, and physical characterization support that the tz2− ligand is a closed-shell planar dianion with unique structural features vastly different from those of the tz, tz˙− and H2tz species.
The unique electronic nature of the 1,2,4,5-tetrazine or s-tetrazine (tz) ring has sparked tremendous scientific interest over the last few years. Tetrazines have found numerous applications, and their ability to coordinate to metal ions has opened the possibility of exploring their chemistry in both molecular systems and extended networks. The rich redox chemistry of s-tetrazines allows them to exchange electrons and switch between their dihydro (H2tz), neutral (tz), and radical (tz˙−) forms. Previous reports in the literature have observed electrochemically that a second electron can potentially be stored in the tetrazinyl ring and form a dianionic species. However, due to its extremely reactive nature, this has not been isolated before. Herein, the combination of strictly anhydrous and inert conditions, strong reducing agents, non-acidic solvents and most importantly blocking the accessibility of the nitrogen atoms by coordinating them to lanthanide ions allowed for the stabilization of a dianionic tetrazine in a lanthanocene complex. Three dinuclear metallocene complexes are reported, [(Cp*2Ln)2(tz˙−)(THF)2](BPh4) (Ln = Y (1-Y); Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) and [(Cp*2Ln)2(tz2−)(THF)2]·2THF (Ln = Gd (2-Gd), or Y (2-Y)), which utilize the unsubstituted tz as the ligand. In 1-Ln, the tz ligand is reduced to the radical anion (tz˙−), while in 2-Ln, the tz ligand is in the −2 charge state. These complexes are the first structurally and physically characterized complexes bearing the dianion radical of an s-tetrazine. Detailed structural analysis, ab initio calculations, and physical characterization support that the tz2− ligand is a closed-shell planar dianion with unique structural features vastly different from those of the tz, tz˙− and H2tz species.
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