2-Aminophenanthrolines Enable the Mild, Undirected Borylation of Alkyl C–H Bonds
The catalytic, undirected borylation of alkyl C–H bonds typically occurs at high reaction temperatures or with excess substrate, or both, because of the low reactivity of alkyl C–H bonds. Here we report a new iridium system comprising 2-anilino-1,10-phenanthroline as ligand that catalyzes the borylation of alkyl C–H bonds with little to no induction period and with high reaction rates. This superior activation and reactivity profile of 2-aminophenanthroline catalysts leads to broader scope of the reaction, including those with sensitive reactants, such as epoxides and glycosidic acetals, enhanced diastereoselectivity, and higher yields of borylated products. These catalysts also enable the borylation of alkanes, amines, and ethers at room temperature for the first time. Mechanistic studies imply that facile N-borylation occurs under the reaction conditions, and that iridium complexes containing N-boryl aminophenanthrolines are competent precatalysts for the reaction.