New routes to, and reactions of polyhedral transition metal carborane species
While in the past few years many complexes of transition metals and carborane ligands have been described, synthetic routes then available were completely dependent on nido- or arachno -carborane derivatives containing nine, and seven boron atoms. In this paper we summarize two new methods which lead to transition metal complexes of carborane ligands. The first of these methods (Polyhedral Expansion) was based upon the formal two or four electron reduction of closo- B n C 2 H n+2 carboranes to form effective ligands containing from six to ten boron atoms. In some cases bimetallic complexes were isolated and polyhedral isomerization reactions were observed in others. The second new method (Polyhedral Contraction) begins with a B 9 C 2 H 11 2- ligand complex and leads to complexes of the B 8 C 2 Y 10 2- and B 7 C 2 H 9 2- ligands by sequential removal of a formal BH 2+ vertex followed by two-electron oxidation to form the next lowest metal complex of the homologous polyhedral series.