Phenylenediamine pyridyl ligands and boryl support ligands for ortho-directed iridium catalyzed c-h borylation

With organoboron compounds being useful components in the synthesis of pharmaceuticals, agrochemicals, and materials, it is imperative to find new catalytic strategies to design an effective system capable of borylating a broad range of (hetero)arene substrates in high yields and high selectivity. Traditional iridium-catalyzed systems borylate aromatic compounds and are directed by steric factors of the substrate. These steric-directed catalysts are hypothesized to have a singly open coordination site on the metal center where activation of the most accessible C-H bond can occur. In order to change regioselectivity from steric products to alternatives, new catalyst systems must be designed. A phenylenediamine pyridyl framework was implemented for chelate-directed C-H borylation, where an aromatic substrate undergoes borylation of the ortho C-H bond, relative to a directing group. This ligand type has been explored and shown to have three major components that influence the reactivity, selectivity, and coordination of the ligand. These parts that make up the ligand were examined using a ligand screen, NMR studies, and stoichiometric reactions. From the literature, it has been shown that double B, N-bidentate ligated catalysts work well for a broad substrate scope and produce borylated products whose substitution pattern is based on steric effects. Other variants of this system have used a single B, N-bidentate ligand to produce products borylated in the ortho-position relative to a directing group on the substrate. To improve upon these catalytic systems, experiments were performed to optimize ortho-selectivity of the originally steric-directed catalyst containing two B, N-bidentate ligands by reducing the loading of the dimer boryl ligand. In doing so, regioselectivities can be completely switched from steric products to chelate products. This modification of ligand to metal ratio greatly effects selectivity and is a unique feature to dimer boryl ligands. These phenylenediamine pyridyl ligands and boryl support ligands will be explored.