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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 (1H,13C,11B), 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 compound4 , which has a vacant C4B2O4cavity, 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 of2 –5 . These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate. -
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 (1H,13C,11B), 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 compound4 , which has a vacant C4B2O4cavity, 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 of2 –5 . These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate.