An Air-Stable, Single-Component\nIridium Precatalyst\nfor the Borylation of C–H Bonds on Large to Miniaturized Scales

The functionalization of C–H bonds enables the\nmodification\nof complex molecules, often with the intention of forming compound\nlibraries. The borylation of aryl C–H bonds is a widely used\nclass of C–H bond functionalization, and conventional catalyst\nsystems for the borylation of C–H bonds consist of an iridium\nsource and an <i>N</i>,<i>N</i>-ligand, in conjunction\nwith pinacolborane, to form the active iridium(III) tris(boryl) catalyst.\nThese multicomponent catalyst systems complicate borylation reactions\nat large and small scales, due to the air sensitivity of the most\ncommon iridium precursor [Ir(cod)OMe]<sub>2</sub>, and, particularly\non small scale, the challenges associated with dispensing multiple\ncomponents with differing solubilities or that are air-sensitive.\nWe describe the discovery of an air-stable, single-component iridium\nprecatalyst, [(tmphen)Ir(coe)<sub>2</sub>Cl], that generates the same\nactive iridium(III) tris(boryl) catalyst and reacts with higher turnovers,\ncomparable selectivity, and similar scope to those of known catalyst\nsystems for the borylation of aryl and heteroaryl C–H bonds.\nWe show how the development of this precatalyst enables reactions\nto be run on submicromole scale in a high-throughput experimentation\nformat in conjunction with ChemBead technology, and with a second\ndiversification step that illustrates the potential to diversify structures\nby chemical sequences involving catalytic reactions, including C–H\nbond functionalizations, on submicromole scales in the same reaction\nvessel.