Aryl boronic esters serve as synthetic intermediates for diverse applications in natural products, agrochemicals, and pharmaceuticals due to the abundance of transformations C–B bonds can undergo. These compounds are commonly synthesized in an atom-economical way by directly converting C(sp2)–H bonds into C–B bonds using Ir-catalyzed C–H borylation (CHB) chemistry. Traditionally, this process favors the C–H bond in the least sterically congested position on substituted (hetero)aromatic ring systems. The work described here unveils novel CHB methods that are competent in targeting specific C–H bonds, thereby enabling the synthesis of a diverse set of compounds. In recent years, a N,B-type dimeric pre-ligand (BB) emerged as the first spectator boryl species capable of steric-directed CHB using a 2:1 ratio of pre-ligand to Ir. Chapter 2 describes how this system was modified to direct borylation ortho to directing groups such as amides and esters by decreasing the ligand to metal ratio to 0.5:1, respectively. Additionally, it was found that maintaining the ligand to metal ratio at 2:1 while switching the Ir(I) pre-catalyst from [Ir(OMe)cod]2 to [IrCl(cod)]2 also led to the generation of chelate-directed products. These methods represent the first instances in which regiochemical switching is achieved by altering the reaction conditions as opposed to the ligand system. The synthesis of the hypothesized pre-assembled catalyst, representing the system where BB loadings are decreased, was isolated and resulted in an Ir(III) cationic species ion pairing with [IrCl2(cod)] as the counteranion. Chapter 3 studies the role of this Ir(I) anionic species in catalysis, detailing a new mode of Ir-catalyzed CHB. This system demonstrates [IrCl2(cod)][NBu4] as a competent catalyst for the transformation of C–H to C–B bonds, independent of external ligand or substrates bearing a directing group. Furthermore, it was found that the site of C–H activation is influenced by the length of the alkyl chain in the ammonium cation, where [NPr4]+ increased the amount of ortho borylated product. Mechanistic experiments suggest this occurring through a heterogenous process that is distinct from classical homogenous CHB reactions that proceed via an Ir(III)/Ir(V) catalytic cycle.
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