Understanding Selectivity and Activity in Z-selective Metathesis with Cyclometallated Ru-based Catalysts

Citation

Quigley, Brendan Liam (2016) Understanding Selectivity and Activity in Z-selective Metathesis with Cyclometallated Ru-based Catalysts. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z96W984J. https://resolver.caltech.edu/CaltechTHESIS:06052016-231830980

Abstract

With the advent of well-defined highly active catalysts, olefin metathesis has become a powerful tool for the formation of carbon–carbon double bonds in a variety of settings. However, these traditional catalysts preferentially form the E-alkene product. Recent efforts have yielded several families of Z-selective metathesis catalysts, including a family of Ru complexes with cyclometallated NHC ligands developed in our group. The work in this thesis describes efforts to develop an improved understanding of the catalyst features that govern activity and selectivity in the cyclometallated Ru-based catalysts, as well as to expand the scope of reactivity in these systems.

Chapter 1 provides an outline of the key features that govern selectivity in cross metathesis applications.

Chapter 2 describes the application of cyclometallated Ru-based catalysts in Z-selective cross metathesis (CM) of allylic-substituted olefins. Efficient CM is demonstrated in the case of acrolein acetals providing a new route to access Z-α,β-unsaturated acetals and aldehydes. For a variety of other allylic-substituted olefins, reactivity was lower but could be correlated with the structure of the catalyst and substrate. The implications of the observed reactivity are discussed and contextualized with regard to reactivity of previous metathesis catalysts.

Chapter 3 describes the development of a series of cyclometallated Z-selective metathesis with varying N-aryl groups that allow elucidation of the key catalyst features that govern activity and selectivity in these systems. The synthesis of the catalyst series is described, including several strategies employed to circumvent unexpected side-reactions. The second part of the chapter focuses on the dynamic behavior of the catalysts in solution and studies of an unusual C–H····F–C intramolecular interaction observed in some of these catalysts. Finally, the reactivity of these catalysts in a variety of CM applications are discussed, which allows for development of a refined model of how the N-aryl group affects Z-selectivity and activity in these catalysts systems and how this varies across different classes of substrate.

Thesis Files