The Hexacyanodiborane(6) Dianion [B2(CN)6]2−

Abstract Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron compounds with an electron‐precise B–B σ‐bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion [B 2 (CN) 6 ] 2− that is chemically very robust is reported. The dianion is air‐stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H 3 O) 2 [B 2 (CN) 6 ] starts at 200 °C. The [B 2 (CN) 6 ] 2− dianion is readily accessible starting from 1) B(CN) 3 2− and an oxidant, 2) [BF(CN) 3 ] − and a reductant, or 3) by the reaction of B(CN) 3 2− with [BHal(CN) 3 ] − (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an S N 2 mechanism.