Direct C(sp2)–H Borylation of Arenes Using Ir-bpy Porous Organic Polymers

Abstract

Organoboron compounds are important building blocks in organic chemistry for a variety of key transformations in the production of compounds in the pharmaceutical and agricultural industries. Direct C–H borylation provides many advantages over more traditional transformation via halide groups that lead to stoichiometric waste. In the direct C(sp2)–H borylation of arenes, Ir-bipyridine systems have shown excellent performance. However, to make the formation of borylated products more benign and greener, transformations catalyzed by heterogeneous catalysts are appealing as they provide easier recovery and reuse of the catalyst. In this study, two different porous organic polymers (POPs) based on polystyrene-bearing bipyridine (bpy) ligands were synthesized. These POPs can, upon metal ligation in situ create an active catalyst that is capable of borylation twice per B2pin2 molecule. Our Ir systems were tested with different arenes, and a preliminary mechanistic investigation was performed. The system was recyclable for up to three consecutive recycles, albeit, the polymer backbone had indications of being borylated during the reaction.