“Umpolung” at Boron by Reduction of [B(CN)₄]⁻ and Formation of the Dianion [B(CN)₃]²⁻

A homoleptic cyanoborate with nucleophilic boron atom: An unprecedented dianion in the salts M2[B(CN)3] (M=Li, Na, K) with nucleophilic boron in the formal oxidation state +1 was obtained by reductive BC bond cleavage in the [B(CN)4]− anion and characterized by NMR (11B, 13C), vibrational spectroscopy and single crystal X-ray diffraction. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.