Date of Award
Spring 2026
Document Type
Open Access Dissertation
Department
Chemistry and Biochemistry
First Advisor
Dmitry V. Peryshkov
Abstract
Transition metal catalysis is a powerful tool for the synthesis and transformation of complex organic molecules, comprising the majority of chemical manufacturing processes and contributing trillions of dollars to the global economy. Often, these catalysts contain precious metals, which have low natural abundance, leading to higher costs. Thus, interest in metal-free catalysis has grown in the last few decades. Compounds containing phosphorus, which has two stable redox states that differ by two electrons, can mimic oxidative addition and reductive elimination processes, providing an alternative for transition metals. Additionally, redox-active clusters, such as carboranes, have been of particular interest in medicinal therapies and ligand design due to their ability to accept two electrons reversibly. Carboranyl diphosphines, the combination of these two main-group classes, have demonstrated the ability to activate numerous small molecules.
This dissertation highlights three main facets of carboranyl diphosphines: the bond activation of small molecules, the ability of the carborane cluster to render electron-rich phosphines electrophilic and thus susceptible to nucleophilic attack, and their use as redox non-innocent ligands with metals, giving rise to unique photophysical properties.
The first two chapters discuss the redox activity of carborane, the established success in oxidative addition-type reactions with carboranyl diphosphines, and the development of strategies to induce reductive elimination-type transformations. Notably, zwitterionic nido-carboranyl diphosphoniums performed transfer hydrogenation reactions via proton-coupled electron transfer (PCET) to quinones, yielding the first example of PCET reactivity with carboranes. This reactivity regenerated a neutral closo-carboranyl diphosphine and converted the quinones to their corresponding hydroquinones. Previous work reported the conversion of an asymmetric closo-carboranyl diphosphine into the zwitterionic nido- derivative upon reaction with main-group hydrides; therefore, the work reported herein represents the complete synthetic cycle for the metal-free reduction of quinones, with the redox-active carboranyl diphosphine scaffold acting as a mediator. Through pKa determination, electrochemical studies, and kinetic isotope effect calculation, further probing revealed the ability of the protons and electrons of the nido-carboranyl diphosphonium to transfer independently, unlocking the possibility for switchable catalysis.
The final two chapters discuss the overwhelming electronic effects imparted by the carborane cluster on the reactivity of carboranyl diphosphines toward nucleophiles, both as standalone compounds and as ligands. This work reports a regioselective nucleophilic attack at phosphorus, which has been rendered electrophilic by efficient overlap of the lone pair with the LUMO within the electron-withdrawing cluster. We also report the synthesis of a bulky carboranyl diphosphine which was previously deemed impossible via manipulation of the redox activity of the cluster. This new diphosphine similarly exhibits electrophilic behavior upon coordination to a gold(I) metal center. A trend of the effects of electron-richness of phosphine groups on the reactivity and optical profiles is established for multiple metal complexes. While traditional literature posits that carboranyl diphosphines act as nucleophiles in bond activation reactions, we aim to establish a rich library of electrophilic pathways that unlock new derivatives without significant side products.
Rights
© 2026, Bryce Christian Nussbaum
Recommended Citation
Nussbaum, B. C.(2026). Exploring and Exploiting the Unique Steric and Electronic Environments of Carboranyl Diphosphines. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/8923