UBC Theses and Dissertations
Factors influencing the rates and selectivity of reductive elimination from high-valent group 10 metal complexes Bowes, Eric G.
This Thesis presents studies of carbon-carbon and carbon-heteroatom reductive elimination from high valent, organometallic group 10 metal complexes in the +III and +IV oxidation states. These fundamental studies advance our understanding of an elementary reaction that is critical to product formation in both well-established and proposed catalytic methods for small molecule functionalization. In Chapter 1, our current understanding of the fundamental aspects of reductive elimination from d6 metal centers is discussed. In addition to providing historical perspective, this Chapter outlines evidence for mechanistic aspects of the reductive elimination reaction, including the influence of ligands and the intermediacy of unsaturated complexes. Chapter 2 presents a study considering the influence of ligand properties on the selectivity between C(sp³)-C(sp³) and C(sp²)-C(sp³) bond formation in reductive elimination from Pt(IV). It is shown that the barriers to both processes are similar such that ligand design strategies can be employed to control the outcome of the reaction. In Chapter 3, a set of small bite angle aminophosphine ligands are prepared and their coordination chemistry with Pt(II) is investigated. Small bite angle ligands enhance the behavior of metal complexes by exhibiting hemilability, promoting the formation of reactive unsaturated intermediates. It is shown that the presence of large phosphorus substituents is necessary for the synthesis of these species. Chapter 4 explores the influence of chelate ring strain on reductive elimination from organometallic Pt(IV) complexes. The aminophosphine ligand set developed in Chapter 3 was used to prepare Pt(IV) complexes with both four- and five-membered chelate rings. Ring strain in the complex featuring the small bite angle ligand was found to promote C(sp³)-C(sp³) RE by lowering the barrier to formation of a five-coordinate intermediate. In Chapter 5, the influence of oxidation state on the selectivity between carbon-carbon or carbon-heteroatom reductive elimination is explored for organometallic nickel complexes in the +III and +IV oxidation states. It is demonstrated the increase in formal oxidation state upon moving from Ni(III) to Ni(IV) results in a change in selectivity from carbon-carbon to carbon-heteroatom elimination. Chapter 6 provides a concise summary of the results presented herein, as well as an outline of future directions for this work.
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