Bulky Bipyridine-Type Ligand-Enabled para-Selective C–H Borylation of Aromatic Compounds

We successfully developed a para-selective C–H borylation of aromatic compounds using iridium catalysts with bulky bipyridine-type ligands. The key to success is the introduction of bulky substituents (m-terphenyl groups) at the 4- and 4′-positions of the bipyridine-type ligands to sterically protect both sides and back of the catalysts, thereby efficiently preventing substrate orientation that gives ortho- and meta-borylated products. Using these ligands, higher para-selectivity was achieved compared to the conventional iridium-catalyzed para-selective C–H borylation. Interestingly, high para-selectivity was achieved even when using aromatic compounds with small substituents such as ethyl or isopropyl groups on the aro-matic ring.