Daniel Marcos Atanes

Bipyridine and phenanthroline are well-established neutral ligands for promoting iridium-catalyzed borylations of aromatic C–H bonds. However, their use with aliphatic substrates is almost uncharted. Herein we demonstrate that introducing CF substituents at the 5- and 5′-positions of bipyridine generates ligands that enable an efficient and regioselective iridium-catalyzed borylation of the methyl group in a broad variety of methylamides. The reaction shows broad functional group tolerance and exhibits remarkable selectivity, offering a powerful approach for the borylation of challenging aliphatic C–H bonds. Mechanistic investigations, including computational analysis, suggest that the accelerating effect of the ligand is likely associated with the formation of non-covalent dispersion interactions between the carbonyl amide of the substrates and the trifluoromethylated pyridine rings of the ligand.

Iridium-catalyzed borylations of aromatic C−H bonds are highly attractive transformations because of the diversification possibilities offered by the resulting boronates. These transformations are best carried out using bidentate bipyridine or phenanthroline ligands, and tend to be governed by steric factors, therefore resulting in the competitive functionalization of meta and/or para positions. We have now discovered that a subtle change in the bipyridine ligand, namely, the introduction of a CF3 substituent at position 5, enables a complete change of regioselectivity in the borylation of aromatic amides, allowing the synthesis of a wide variety of ortho-borylated derivatives. Importantly, thorough computational studies suggest that the exquisite regio- and chemoselectivity stems from unusual outer-sphere interactions between the amide group of the substrate and the CF3-substituted aryl ring of the bipyridine ligand.