UC Berkeley

Chapter 1. The field of f-block–transition metal hydride chemistry is introduced and summarized. Key properties of these compounds such as small molecule activation chemistry and H2 uptake and release are outlined. The dearth of actinide–transition metal species despite their potential for fundamental bonding insight and novel reactivity is highlighted, and the motivations for studying these compounds are stated.

Chapter 2. Reaction of K[Cp*IrH3] with actinide halides led to multimetallic actinide–transition metal hydrides U{(μ-H)3IrCp*}4 and Th{[(μ-H)2(H)IrCp*]2[(μ-H)3IrCp*]2}, respectively. These complexes feature an unexpected, significant discrepancy in hydride bonding modes; the uranium species contains twelve bridging hydrides while the thorium complex contains ten bridging hydrides and two terminal, Ir-bound hydrides. Use of a U(III) starting material with the same potassium iridate resulted in the octanuclear complex {U[(μ2-H)3IrCp*]2[(μ3-H)2IrCp*]}2. Computational studies indicate significant bonding character between U/Th and Ir in the tetrairidate compounds, the first reported evidence of actinide-iridium covalency. In addition, these studies attribute the variation in hydride bonding between the tetrairidate complexes to differences in dispersion effects. This work establishes a novel route to synthesizing actinide–transition metal polyhydrides with close metal–metal contacts.

Chapter 3. Conversion of Cp*OsH5 to K[Cp*OsH4] with KBn, followed by reaction with tetravalent actinide halides results in the synthesis of uranium– and thorium–osmium heterometallic polyhydride complexes. Through these species, An–Os bonding and the reactivity of An–Os interactions are studied. These complexes are formally sixteen-coordinate, the highest observed coordination number for uranium and thorium. Computational studies suggest the presence of a significant bonding interaction between the actinide center and the four coordinated osmium centers, the first report of this behavior between osmium and an actinide. Upon photolysis, these complexes underwent intramolecular C–H activation with the formation of an Os–Os bond, while the thorium complex was able to activate an additional C–H bond of the benzene solvent, resulting in a μ-η1,η1 phenyl ligand across one Th–Os interaction. These results highlight the unique reactivity that can arise from actinide and transition metal centers in proximity, and expand the scope of actinide photolysis reactivity.

Chapter 4. The third Cp*-supported transition metal polyhydride – Cp*ReH6 – was shown to be a competent partner to actinide hydrides. The synthesis of actinide tetrarhenate complexes completed a series of iridate, osmate, and rhenate polyhydrides, allowing for structural and bonding comparisons. Computational studies examine the bonding interactions, particularly between metals, in these complexes. Several factors affect metal–metal distances and covalency for the actinide tetrametallates, including metal oxidation state, coordination number, and dispersion effects. The osmium and rhenium octametallic U2M6 clusters are reported as well, with similar analysis of structure and electronics.

Chapter 5. Reaction of the potassium iridate K[Cp*IrH3] with a bulky uranium(III) metallocene yielded a heterobimetallic U(III)–Ir species. Reactivity of this complex with CS2 is described, resulting in the novel ethanetetrathiolate fragment, as produced via hydride insertion and C–C coupling. This demonstrates the ability to combine the hydride insertion chemistry of transition metal hydrides with C–C coupling observed in U(III) compounds by bringing both metal centers in close proximity.