Approaching Dianionic Tetraoxadiborecine Macrocycles: 10‐Membered Bora‐Crown Ethers Incorporating Borafluorenate Units. Issue 5 (27th December 2022)

• Record Type: Journal Article
• Authors: Wentz, Kelsie E.; Molino, Andrew; Freeman, Lucas A.; Dickie, Diane A.; Wilson, David J. D.; Gilliard, Robert J.
• Is Part Of: Angewandte Chemie international edition. Volume 62:Issue 5(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-27
• Subjects: Borafluorene -- Boron -- Crown Ether -- Ionophores -- Oxaboracycles; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202215772
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: The addition of non‐benzenoid quinones, acenapthenequinone or aceanthrenequinone, to the 9‐carbene‐9‐borafluorene monoanion (1 ) affords the first examples of dianionic 10‐membered bora‐crown ethers (2 –5 ), which are characterized by multi‐nuclear NMR spectroscopy ( 1 H, 13 C, 11 B), X‐ray crystallography, elemental analysis, and UV/Vis spectroscopy. These tetraoxadiborecines have distinct absorption profiles based on the positioning of the alkali metal cations. When compound 4, which has a vacant C4 B2 O4 cavity, is reacted with sodium tetrakis[3, 5‐bis(trifluoromethyl)phenyl]borate, a color change from purple to orange serves as a visual indicator of metal binding to the central ring, whereby the Na + ion coordinates to four oxygen atoms. A detailed theoretical analysis of the calculated reaction energetics is provided to gain insight into the reaction mechanism for the formation of 2 –5 . These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate. Abstract : The first examples of dianionic tetraoxadiborecines are isolated via the reaction between 9‐carbene‐9‐borafluorene monoanion and non‐benzenoid quinones. Remarkably, the bora‐crown ether ring is able to capture a sodium ion from sodium tetrakis[3.5‐bis(trifluoromethyl)phenyl]borate. Additionally, the position and/or binding of the metal ions to the bora‐crown are easily observable via specific color changes.