"In homogeneous transition metal catalysis, the precatalyst usually needs to undergo a series of rearrangements or changes in the coordination sphere to form the active catalyst, which is responsible for the desired transformation. Isolation of these active intermediates along with mechanistic studies would provide greater insight to how the transformation works and would be extremely beneficial for modifying and designing a new catalyst/ligand system. In Ir-catalyzed C-H activation/borylation, 5-coordinate iridium boryl species are reported to be the active catalytic species. Despite the initial report for utilizing phosphine ligands in thermal catalytic aromatic C-H borylation, bidentate nitrogen donor ligands have been used more frequently due to their higher reactivity.1 To analyze the origin of this difference, we studied a previously reported 5-coordinate iridium trisboryl complex stabilized by a bidentate phosphine ligand, which reacts directly with sp2 C-H bonds, providing a rare opportunity for examining the fundamental step in C-H borylation. Previously, this complex had been shown to react stoichiometrically at room temperature, but under catalytic conditions elevated temperatures were required. We have found that the 16 electron 5-coordinate trisboryl complex and HBpin are in equilibrium with generating a six-coordinate borylene complex, which is the dominant species at the outset of the reaction. As borylation commences during the catalytic reaction, the H2 produced from C-H activation converts the borylene to a series of intermediates. These intermediates represent multiple resting states of C-H borylation catalyst, which operate in parallel catalytic cycles. The complexes were isolated and characterized by 31P and 1H NMR, and X-ray crystallography, making this the most fully characterized catalytic system for C-H borylation described to date. Insights from these studies are being used to design new bidentate catalysts for sp2 and sp3 C-H functionalizations. In the second part of this dissertation, ortho directed C-H borylation of aromatic compounds will be discussed. In our novel approach without need of installation and removal of directing or protecting group, borylation of benzoates, benzamides, ketones, anisoles, and phenyl pyridines occurs ortho to the functional group. In this systems, 14- electron intermediates likely mediate these processes. We have shown that low-coordinate Ir precatalysts can be obtained by using donor ligands that incorporate pendant silanes. These species are active for directed C-H borylations with a range of substrates. We will discuss mechanisms by which these catalysts operate, present structures that pertain to catalysis, and discuss substrate scope in the context of other methodologies."--Pages ii-iii.
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