Heterodicarba-nido-hexaboranes from Hydroborations of Exocyclic Unsaturated Heterodiborolanes

Abstract

The hydroboration of 1-aza-2,5-diduryl-3,4-diisopropylidene- and 2,5-diduryl-1-thia-3,4-diisopropylidene-2,5-diborolanes (1b, 2b) with equimolar amounts of BH3·thf leads to the corresponding 2-aza-4,5-dicarba- and 4,5-dicarba-2-thia-nido-hexaboranes 3c and 4e. When an excess of BH3·thf reacts with the azadiborolane 1b the azadiborole derivative 5 is obtained as the main product. This surprising result is explained by the addition of three BH3·thf moieties and the subsequent loss of B3H7·thf. The reaction of the sterically less hindered tert-butylazadiborolane 1c with BH3·thf yields two 2-aza-4,5-dicarba-nido-hexaboranes (3d,e), both of which carry a tBu group in the apical position. A possible reaction pathway is suggested. The new heterocarboranes 3c,d,e and 4e are identified by multinuclear NMR spectroscopy and mass spectrometry. X-ray crystallographic studies of 3c and 4e confirm the nido-arrangement of the cluster atoms.