Boron: Polyhedral Metallaboranes

Abstract

Metallaborane clusters and their related chemistry were initially developed as a variant of metal–ligand coordination chemistry much along the lines of organometallic chemistry. However, owing to the insight imparted by the electron counting rules and isolobal analogy principle, the interconnections between apparently distinct molecules like polyhedral boranes and transition metal clusters were established. This certainly defined the scope of the area and notable advances toward the improvement of synthetic routes were witnessed. The advent of improved routes for synthesis widened the purview further by extending the limits of attainable sizes and geometries of polyhedral metallaboranes from diborane analogs to polyhedral cages of up to 12‐vertices to supraicosahedral and condensed cage macro‐polyhedral clusters. Wade–Mingos rules and Jemmis mno rule helped at gaining perspective about the unique structure and bonding present in this class of compounds. This article provides a brief overview of the syntheses and structural aspects in the context of electron counting rules of the most noted structural motifs assumed by polyhedral metallaboranes.