N-Heterocyclic Olefins: Applications in Catalysis and Low-Coordinate Element Stabilization

Abstract

The work in this Thesis outlines the use of N-heterocyclic olefins (NHOs) as organocatalysts, as supporting ligands in palladium-catalyzed cross-coupling, and the development of anionic NHOs as ligands for main group element and transition metal centers. N-Heterocyclic olefin-hydridodiborane complexes were synthesized with the aim of performing the catalytic hydroboration of ketones and aldehydes with pinacolborane. These NHO-hydridodiborane complexes were not active catalysts, but the precursor NHOs were the catalyst in the hydroboration of ketones and aldehydes. New NHOs were synthesized and explored as supporting ligands in BuchwaldHartwig aminations. Through a combination of imaging, poisoning, and kinetic experiments, it was determined that a well-defined NHO-supported Pd0 complex was not the active catalyst, but palladium nanoparticles formed in situ. NHO-AlR3 Lewis acid-base adducts were shown to catalyze the polymerization of acrylic Michael-type monomers via a frustrated Lewis pair mechanism. A two-coordinate zinc(II) complex supported by anionic N-heterocyclic olefin (aNHO) ligands was synthesized and was shown to undergo transmetallation with main group element halides and hydrides. Group 4 and Group 8 metal centers were also stabilized by aNHO ligands.