UC Berkeley

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.