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The Application of Carborane Anions in Ligand Design and Materials Development


Since the discovery of polyhedral boranes, these molecules have expanded from items of molecular curiosity to having a wide scope of applications in contemporary chemistry. Borane clusters range in size and shape and can possess various heteroatoms. The term ‘carborane’ denotes a class of borane clusters containing one or more carbon atom in the polyhedral boron framework. Carboranes are structurally and electronically unique; while the carbon and boron atoms appear to exceed normal bonding configurations, these atoms are actually participating in delocalized bonding throughout the cluster. During the Cold War, the American government invested in rocket propulsion fuels featuring clusters primarily composed of boron, but the fuels were ultimately determined to be impractical. As the rush for boron fuel came to an end, research performed on borane clusters was published in the early 1960’s, revealing the first carboranes. The work presented here utilizes two different anionic carboranes: the 12-vertex cluster, carba-closododecaborate anion (HCB11H11-), and the smaller 10-vertex cluster, carba-closo-decaborate anion (HCB9H9-). Each anionic cluster possesses an overall charge of -1 delocalized throughout the 3-dimensional cluster, contributing to the tremendous stability of these structures. Substitution of the clusters’ hydride substituents with halides renders the carboranes even more weakly coordinating and much less susceptible toward chemical decomposition.

A large component of this work addresses the incorporation of both the 10 and 12- vertex carborane anions into ligand motifs. Carborane clusters are not typically included in catalyst design, and since the 1960’s there have been only a few investigations exploring the applications of carboranes in ligand development. Carboranes are excellent synthons for constructing covalently bonded, architecturally novel molecules whose electronic and steric properties can be tailored to specific purposes. Beyond their use in ligand design, this thesis also contains work developing carborane-functionalized materials. Due to the charged nature of the carboranes, they are ideal building blocks for ionic liquids. Carboranes possess an array of favorable properties and the goal of the work presented in this thesis is to contribute to a more comprehensive understanding of these unique molecules.

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