Synthesis and Reactivity of Anthracene-Based Molecular Precursors for Low-Valent Boron Species

Abstract

The study of compounds containing elusive main group multiple bonds has long been a topic of immense interest. Today, it remains an attractive path towards unlocking new reactivity and developing a complete empirical understanding of chemical bonding. However, due in large part to a lack of suitable synthetic methodologies, the chemistry of numerous desirable functionalities remains poorly accessible. Herein, we report the synthesis of the first series of dibenzo-7-boranorbornadienes, or 9,10-bridged boron anthracene (RBA, A = anthracene or C₁₄H₁₀) compounds, and their unique properties and reactivity. Oxidation of ⁱPr₂NBA with an amine oxide was found to lead to the selective formation of the bicyclic borinate ester ⁱPr₂NBOA, an easily isolable solid that unimolecularly fragments to ⁱPr₂NBO + A upon heating to moderate temperatures in solution. This rare free, monomeric oxoborane has been demonstrated to undergo cycloadditions with a number of organic substrates and efforts to expand both the scope of derivatives and reactivity are underway. The possibility to access species containing highly unstable boron-pnictogen triple bonds has also been explored via the synthesis of the azidoborane trimer (N₃BA)₃ and cyclic(alkyl)(amino)carbene (CAAC) stabilized boraphosphaketene ᵉᵗCAAC·ABPCO. Preliminary and ongoing reactivity studies are discussed.