<i>hypercloso</i>‐Hexa(amino)hexaboranes: Structurally Related to Known <i>hypercloso</i>‐Dodecaboranes, Metastable with Regard to Their Classical Cycloisomers

Abstract

Abstract B 6 (NMe 2 ) 6 ( 2a ) is the first neutral hypercloso ‐hexaborane to be characterized by X‐ray structural analysis. The geometry of 2a is in nice agreement with that of the C i symmetric molecule computed at the B3LYP/6‐311+G** level of theory. Two B 3 triangles with long B ··· B distances in 2a are reminiscent of those in Hawthorne's benzyloxy‐substituted hypercloso ‐dodecaboranes 6a , b . Upon heating to 200 °C, 2a transforms into Nöth's classical cyclohexaborane 1a . Computations at the B3LYP/6‐311+G** + ZPE level of theory show 1a to be 21.6 kcal mol –1 lower in energy than 2a , that is, the latter is metastable. hypercloso ‐Hexaborane B 6 (NEt 2 ) 6 ( 2b ), which was reported to be thermodynamically more stable than 1b , is computed to be 22.4 kcal mol –1 less stable than 1b . Pure 1b is shown here not to transform into 2b upon standing in solution, which is in contrast to reports in the literature for a mixture containing 1b . (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)