AZA-CLOSO-DODECABORANE(12) - THE STORY OF 6-COORDINATE NITROGEN

The icosahedron-type closo-aza- and closo-azainetalladodecaboranes NB1 1H12 and MNB10H11 and the corresponding neutral and anionic nido-azaun decarboranes NB10H13, NB10H12- and NB10H12- arc described. These speci es are the isoelectronic analogues of the well known dicarbaboranes C2 B10H12, MC2B9H11, C2B9H13, C2B9H12-, C2B9H112-, closo-Azadodecaboranes arc the first examples of nitrogen incorporated in a cluster skeleton with five-fold connectivity and six-fold coordination, including the exo-hydrogen atom. Several methods for the synthesis of the closo- and nido-azaboranes are reported. The structure of NB11H12 is discussed. The nido-anion NB11H12X-, which is the product Of opening closo-NB11H1 2 by the action of a base X-, is interpreted in terms of the related h ypothetical 13-vertex polyhedron NB12H13.