UBC Theses and Dissertations

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UBC Theses and Dissertations

1,3-N,O-Chelated early-transition-metal complexes for the activation and formation of C−E (E = H, C, N, O) bonds Griffin, Samuel Elliot


This thesis describes the exploration of 1,3-N,O-chelated early-transition metals and their applications in diverse catalytic reactions. While cyclopentadienyl-ligated metal complexes and their derivatives are highly robust and have found extensive catalytic applications in industry, their robustness limits their ability to act cooperatively with the metal centre to promote new and challenging transformations. In addition, the multi-step synthetic routes required to access modified cyclopentadienyl derivatives hinder tuning of the steric and electronic properties as needed. 1,3-N,O-chelating ligands are complementary to cyclopentadienyl ligands as a result of their highly modular syntheses and unsymmetrical donor properties, leading to flexible coordination modes, hemilability, and potential for metal-ligand cooperativity. However, 1,3-N,O-chelating ligands are comparatively underexplored despite promising recent advances in catalysis. Chapter 2 describes the use of zirconium ureate complexes for the catalytic hydroamination of 2-vinylpyridine. Stoichiometric and mechanistic studies revealed that the reaction with 2-vinylpyridine proceeds through an aza-Michael mechanism, where the C−N bond forming step is reversible and can be directly observed by variable temperature 1H NMR spectroscopy. In Chapter 3, these zirconium ureate complexes were investigated for their reactivity in hydroaminoalkylation. This led to the discovery of the first catalytic example of hydroaminoalkylation with alkyne substrates to directly access allylic amines. Stoichiometric and mechanistic studies suggest that the open coordination sphere of the zirconium catalyst aids in promoting the challenging reaction steps necessary for catalytic turnover. Chapter 4 investigates the coordination chemistry and reactivity of vanadium pyridonate complexes, which were previously unexplored. These compounds can be made easily via protonolysis of amido or organometallic starting materials, as is the case for other early-transition metal pyridonates. Vanadium(IV) pyridonates were found to undergo reduction to vanadium(III) in some cases, and mechanistic studies found that the released alkylamine during protonolysis was acting as the reductant. These compounds also showed hemilability, potential for metal-ligand cooperativity, and a tendency to aggregate. Chapter 5 then discusses the application of vanadium pyridonate complexes in the catalytic reductive coupling of alcohols. Mechanistic studies showed that bimetallic intermediates were involved, providing complementary experimental evidence for the mechanism proposed by DFT in a reported monometallic catalyst system.

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