Chapter one discusses the synthesis and characterization of novel complexes of the uranyl(VI) ion with a substituted phenanthroline ligand ph2phen. The complexes are investigated by electronic and vibrational spectra and their solid-state structures are presented. Luminescence spectra and lifetimes are determined. Density functional theory (DFT) calculations are carried out to investigate the electronic structure of the complexes in the ground and excited states.

Chapter two discusses the photocatalytic reactivity of the new uranyl complexes in alkane fluorination, oxidation and C-C coupling reactions. Visible light mediated functionalization of the C-H bond in the substrate is achieved through hydrogen atom abstraction. The identity of the photocatalyst is investigated for the fluorination reactions. DFT calculations are performed to compare reaction energy barriers for different photocatalysts and gauge the interactions between the substrate and ph2phen ligand. Finally, Stern-Volmer analyses are performed to determine the nature of collisional quenching between the substrate and the photocatalyst.

Chapter 1 reports dinuclear actinide (An) complexes supported by the meta-phenyl-bridged tetraphenolate ligand mTP, and their ability to catalyze the N2 reduction reaction (N2RR). The bis-UIV metallacycle [U2(mTP)2] (1.1) possesses a rectangular, ‘letterbox’-shaped cavity between the two UIV cations. When treated with potassium reductant, 1.1 can mediate the reduction of N2 by four electrons; concomitant intramolecular deprotonation of ligand benzylic C–H leads to the formation of a hydrazido [N2H2]2− ligand in K4[U2(μ-η2:η2-N2H2)(mTP−)] (1.3). We also demonstrate that 1.1 can catalyze the selective formation of HN(SiMe3)2, a secondary silylamine, from N2 under ambient conditions, the first catalyst to achieve this transformation. This also represents the first example of a homogeneous f-block N2RR catalyst. A possible reaction mechanism, which was computed via DFT by our collaborator, is discussed.

Chapter 2 extends our investigation in f-block-mediated N2RR to the lanthanides (Ln). The bis-SmIII metallacycle K2[Sm2(mTP)2(THF)2] (2.1) is also capable of catalyzing the N2RR, the first 4f complex to do so. Compared to 1.1, 2.1 catalyzes the formation of the tertiary silylamine N(SiMe3)3 from N2. This suggests that the N2RR catalyzed by 2.1 is mechanistically different to that by 1.1, in that the mTP benzylic C–H is not deprotonated. The bis-SmIII platform complex [Sm2(mTP)I2(THF)6] (2.2) converts to 2.1 under the reaction conditions, further reinforcing the significance of the metallacyclic geometry in this system. Surprisingly, a wider series of dinuclear platform complexes [Ln2(mTP)I2(THF)n] (2.3; Ln = La, Nd, Dy, Lu), [Th2(mTP)Cl4(THF)5(dme)] (2.4) and [U2(mTP)I4(THF)4] (2.5) can also mediate the N2RR, despite showing no evidence of interconversion to metallacyclic complexes. Preliminary characterization data of the reduced N2 species are discussed, including EPR spectroscopy and magnetic susceptibility measurements that suggest the existence of a ligand radical.

Chapter 3 describes a series of An(IV) complexes supported by the pTP ligand, the para-phenyl-bridged counterpart of mTP. In the absence of donor solvents, the mononuclear complexes [An(pTP)] (An = Th 3.1, An = U 3.2) are formed, in contrast to the dinuclear mTP complexes described in Chapter 1. Both 3.1 and 3.2 possess rare η6-AnIV–arene interactions, which were investigated both experimentally, and computationally via DFT by our collaborators. Electronic structure calculations of the reduced analogues [3.1]− and [3.2]−, as well as the isoelectronic Yb counterpart [Yb(pTP)]− (3.15), were able to locate the unpaired electron density in each case and identify potential molecular qubit candidates. Addition of Lewis bases and monoanionic ligands also allowed us to study the effect of axial donor strength.

Chapter 4 investigates the application of the mTP ligand in stabilizing the uranyl(VI) dication, (UO2)2+. The platform complex [(UO2)2(mTP)(THF)3] (4.1) and metallacyclic [Na(15-c-5)(py)]4[(UO2)2(mTP)2] (4.5) were synthesized and fully characterized, locating two uranyl dications in close proximity. The U(VI) to U(IV) reduction of 4.1 can be mediated by the simple f-block halide SmI2(THF)2, but is concomitant with ligand dissociation. Complex 4.1 is also capable of mediating hydrogen atom abstraction reactions from hydrocarbons under visible light irradiation.

Chapter 1. To date, the exploration of ligands that can support cerium, or any other lanthanide (Ln), in photocatalysis has been limited to halides, pseudohalides, and simple nitrogen donors. No organometallic photocatalyst has yet been reported that combines the photoexcitable cerium cation with strongly binding, multifunctional, tunable ligands. This chapter conveys the synthesis and characterization of a range of cerium photocatalysts, alongside a new family of photoactive Ln(III) compounds (Ln = La, Nd, Sm) supported by a light-absorbing tunable aryloxide-tethered N-heterocyclic carbene (NHC), tetramethylcyclopentadienyl (CpMe4), and pseudohalide ligands. The synthesis and characterization of the trivalent uranium analogue of these species is also presented, alongside investigation into the photophysical properties of select complexes.

Chapter 2. The complexes described in Chapter 1 are capable of the rare, selective,photocatalytic C–F bond functionalization of sp3 hybridized C–F bonds, when used in conjunction with magnesium alkyl reagents. The work described in this chapter is, to the best of our knowledge, the first example of catalytic C–F bond activation and functionalization mediated by a rare-earth metal complex. Ligand light-absorption and redox non-innocence allows for the photocatalysis to be accessed even by typically photo- and redox-inactive metals including lanthanum and magnesium. Through a combination of experiment and theory, this work provides unique insight into the cooperativity between metal and ligand in photocatalysis, and the significance of ligand redox-non innocence in radical mechanisms.

Chapter 3. The studies described in Chapter 2 of this thesis conclude that specialized, light- absorbing aryloxide ligands are required for the efficient photocatalytic cleavage of strong C– F bonds by Ln complexes. In this chapter, trivalent Ln tetramethylcyclopentadienyl complexes (Ln = La, Ce, Pr, Nd, Sm) are shown to photochemically activate the weaker sp3 carbon– chlorine bond of chlorinated hydrocarbons via a reactive lanthanide alkyl species. Becauselight absorption by the CpMe4 ligand is efficient, photocatalytic reactivity is enhanced for cerium and possible for neighboring, normally photoinactive, Ln congeners. Calculations are utilized to further understand the mechanism of this process, and preliminary results in the catalytic dechlorination of polyvinyl chloride (PVC) are presented.