Forming B–B Bonds by the Controlled Reduction of a Tetraaryl-diborane(6)

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• 作者：Thomas Kaese ; Alexander Hübner ; Michael Bolte ; Hans-Wolfram Lerner ; Matthias Wagner
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：May 18, 2016
• 年：2016
• 卷：138
• 期：19
• 页码：6224-6233
• 全文大小：642K
• 年卷期：0
• ISSN：1520-5126

文摘

Dimeric aryl(hydro)boranes can provide suitable platforms for the synthesis of boron-containing graphene flakes through reductive B–B coupling. Two-electron reduction of 1,2:1,2-bis(4,4′-di-tert-butyl-2,2′-biphenylylene)diborane(6) (4) with LiNaph/THF establishes a B–B σ bond but can be accompanied by substituent redistribution. In the singly rearranged product, Li₂[6], only one 1,2-phenyl shift has occurred. The doubly ring-contracted product, Li₂[7], consists of two 9H-9-borafluorenyl moieties that are linked via their boron atoms. When the amount of LiNaph/THF is increased to 4 equiv, Li₂[6] is subsequently observed as the dominant species. Addition of 11 equiv of LiNaph/THF results in over-reduction with hydride elimination to afford the doubly boron-doped dibenzo[g,p]chrysene Li₂[1]. In contrast, excess KC₈ reduces 4 to the corresponding dihydro-dibenzo[g,p]chrysene, K₂[5], with a trans-HB–BH core. Hydride abstraction from K₂[5] with 1 equiv of 4 leads to K[8], in which the central B–B bond is bridged by a single hydrogen atom. K[8] is also obtained upon treatment of 4 with 1 equiv of KC₈. All products have been characterized by multinuclear NMR spectroscopy and X-ray crystallography.