Abstract
The behavior of Lewis acidic metal ions in multimetallic systems has become a subject of intense interest in recent years. Investigations in this area are inspired by the functioning of Nature’s oxygen-evolving complex (OEC) in Photosystem II, which features a redox-inactive Ca2+ ion involved in reduction potential modulation. In Part I of this dissertation, synthetic, structural, spectroscopic, and electrochemical findings are described for the elucidation, parametrization, and effective leveraging of Lewis acid effects in heterobimetallic complexes of a d-block element, nickel, and an f-block element, uranium. Incorporation of Lewis acidic metal ions into heterobimetallic complexes for chemical and electrochemical tuning has typically focused on d-block elements, but here, this strategy was applied to uranium for the first time. In particular, the redox properties of the uranyl ion (UO22+) have been optimized through formation of heterobimetallic complexes, an outcome needed for development of next-generation nuclear fuel reprocessing technologies. To accomplish this goal, nickel and uranyl complexes were divergently prepared with macrocyclic Reinhoudt-type ligands featuring pendant crown-ether-like sites that readily bind a wide range of redox-inactive metal cations (M = Cs+, Rb+, K+, Na+, Li+, Ca2+, Nd3+, and Y3+). This divergent strategy, enabled by deliberate preparation of appropriate monometallic precursor complexes, affords unique access to complexes with highly Lewis-acidic trivalent cations, a class of compounds that have previously been inaccessible. Through electrochemical determination of thermodynamic reduction potentials, heterogeneous electron transfer rate constants, and reorganization energy values associated with the UVI/UV redox manifold, quantitative trends were measured and used to formulate a mechanistic framework for optimized uranyl redox cycling and design rules for supramolecular structures that promote efficient electrode-driven actinide chemistry. In Part II of this dissertation, the development of tunable heterobimetallic catalysts for ethylene polymerization and preparation of heterobimetallic complexes with diimine-dioxime-type ligands are discussed. Such chemistries can be understood in the context of the general strategy of incorporating Lewis acidic redox-inactive metals, in that multiple metals are found to operate synergistically in all the systems described here. Taken together, the findings described in this dissertation show that interactions with Lewis acids can be used for the rational tuning of the properties of elements across the periodic table.