Evolution of C2B4 Carborane Chemistry: from Early Years to the Present

A review of the chemistry of polyhedral cluster complexes in which s-, p-, dand f-block metals are incorporated mainly into Ccage-trimethylsilyl-substituted C2B4 carborane cages is presented. While the main thrust of this review is on the results obtained in authors’ laboratories, comparisons are made to similar systems and to those involving both largeand small-cage carboranes. In this way we hope to demonstrate the unique chemistry of the small-C2B4-cage systems that has emerged over the last 40 years. However, a full picture of the chemistry of these systems cannot be presented without heavy reference to the larger, more stable 11and 12-vertex cages, which in many ways preceded their more diminutive cousins. The focus of much of the current research is directed toward systematizing the chemistry of metallacarboranes with the aim of promoting their use as possible electronic, ceramic, and/or catalytic materials. However, such endeavors are based on our knowledge about the fundamental interactions that are at work in determining the structures and properties of these cluster complexes. This review attempts to provide such an overview of small-cage heterocarborane chemistry.