Iron-Catalyzed Miyaura Borylation of Aryl Chlorides and Triflates

Simple aryl chlorides represent challenging substrates in iron-catalyzed borylation. A combination of Li[B(tBu)pin-Bpin] as the borylating reagent and a catalyst formed in situ from iron(II) triflate and the commercially available N-heterocyclic carbene ligand, IMes, gives significantly improved activity and a much broader scope than previously reported iron-based catalysts. Iron triflate is also a good precatalyst for the borylation of aryl triflates-a previously unreported transformation-and in these cases the IMes ligand is not required.