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Antimony and Tellurium Non-Innocent Z-Ligands for Transition Metals and Their Application in Photoredox Chemistry and Electrophilic Catalysis
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Ligand design has been an often pursued strategy to advance the development of transition metal complexes for catalysis and activation of small molecules. In the past decade, polydentate Z-type ligands have been recognized as versatile tools to expand on the reactivity of transition metals. The interest generated by polydentate Z-type ligands mainly arises from the ability of the Lewis acidic Z site to behave as σ-acceptor, which can modulate the electronic properties of the metal and impart reactivity to the metal via flexible metal→Z ligand interaction. Group 13 compounds, notable for their Lewis acidity, have been dominating the field of Z-type ligand chemistry, leading to a plethora of discoveries in small molecules activation and organic transformation catalysis. In recent years, heavy main group antimony and tellurium compounds made their unique entry into the Z-type ligand family owing to their Lewis acidity and redox activity. In particular, it was demonstrated that weak donating stibine and telluroether ligands can be switched into σ-accepting Z-type ligands by post-synthetic conversion to their hyper-valent state. Although these phenomena are of fundamental importance, attempts to use these metal complexes for metal catalyzed processes or chemical transformations have not been explored. To fill this knowledge gap, it became the objective of this dissertation to investigate new versions of antimony or tellurium ligand systems and probe their use for the design of late transition metal-based catalysts With this in mind, I chose to investigate halogen functionalized antimony ligands, with augmented Lewis acidity due to the electronegativity of the halogen atoms. The strong Lewis acidity of the halostibine antimony center, coupled with its capacity to undergo oxidation reactions or anion exchanges, led to the isolation of trihalostiborane-gold complexes and trihalostiborane-platinum complexes, featuring magnified metal→Sb(V) interactions. These complexes have been exploited in the development of ligand-centered redox-controlled catalysis, highlighting their utility in the area of smart catalyst design. Another noteworthy result of this research includes the discovery of redox active antimony-platinum molecular platform, in which the halogenated antimony ligand is able to modulate the electron density of the coordinated platinum, thereby facilitating the two-electron redox reactions. Such redox reactions have been utilized to realize the high-quantum-yield photoreductive elimination of chlorine, which is of relevance to photocatalytic production of H2 from HX. In parallel to the antimony chemistry, tellurium ligand chemistry has also been investigated. Our results in this area show for the first time the redox non-innocent behavior of telluroether ligand in the coordination sphere of gold.
Yang, Haifeng (2016). Antimony and Tellurium Non-Innocent Z-Ligands for Transition Metals and Their Application in Photoredox Chemistry and Electrophilic Catalysis. Doctoral dissertation, Texas A & M University. Available electronically from