Recent developments in the chemistry of the nine-vertex monocarbaboranes

A short review is presented on the routes to the synthesis of the nine-vertex monocarbaboranes arachno-4-CB8H14 and nido-1-CB8H12, which now have become very important starting materials for the preparation of a family of ‘smaller-cage’ seven-, eight-, and nine-vertex closo monocarbaborane anions [2-CB6H7]−, [1-CB7H8]−, and [4-CB8H9]−. These anions exhibit high stability and have a good chance to become new candidates for weakly coordinated anion chemistry. Discussed are also reactions leading new families of phosphamonocarbaboranes that contain one, two, and three phosphorus atoms in the cage. These compounds, namely closo-2,1-PCB8H9, closo-6,1-PCB8H9, nido-7,8,9-P2CB8H10, and nido-7,8,9,10-P3CB7H8, are structural analogues of the corresponding carboranes and are likely to exhibit similar chemical behavior.