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  1. 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 (25), 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 of25. These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate.

     
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  2. Abstract

    Borepin, a 7‐membered boron‐containing heterocycle, has become an emerging molecular platform for the development of new materials and optoelectronics. While electron‐deficient borepins are well‐established, reduced electron‐rich species have remained elusive. Herein we report the first isolable, crystalline borepin radical (2 a,2 b) and anion (3 a,3 b) complexes, which have been synthesized by potassium graphite (KC8) reduction of cyclic(alkyl)(amino) carbene‐dibenzo[b,d]borepin precursors. Borepin radicals and anions have been characterized by EPR or NMR, elemental analysis, X‐ray crystallography, and cyclic voltammetry. In addition, the bonding features have been investigated computationally using density functional theory.

     
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