Frustrated Catalyst Activates C–H Bonds

A new technique activates heteroarene C–H bonds in a new way: with a frustrated Lewis pair. In such compounds, an electrophile (Lewis acid) and nucleophile (Lewis base) that would normally react with one another are blocked (“frustrated”) from doing so. The leading heteroarene C–H activation approach is transition-metal catalysis. Frédéric-Georges Fontaine and coworkers at Quebec’s Laval University have now identified a borane-based frustrated Lewis pair that can catalytically activate C–H bonds of furans, thiophenes, and pyrroles to form boronates (Science 2015, DOI: 10.1126/science.aab3591). The catalyst’s nucleophilic amine abstracts a heteroarene C–H proton, and its electrophilic borane complexes with the C–H carbon, promoting borylation. The nonmetal catalyst avoids metal cleanup of products and can catalyze some reactions transition metals can’t handle easily.