Markovnikov-Selective, Activator-Free Iron-Catalyzed Vinylarene Hydroboration

Two series of structurally related alkoxy-tethered NHC iron­(II) complexes have been developed as catalysts for the regioselective hydroboration of alkenes. Significantly, Markonikov-selective alkene hydroboration with HBpin has been controllably achieved using an iron catalyst (11 examples, 35–90% isolated yield) with up to 37:1 branched:linear selectivity. anti-Markovnikov-selective alkene hydroboration was also achieved using HBcat and modification of the ligand backbone (6 examples, 44–71% yields). In both cases, ligand design has enabled activator-free low-oxidation-state iron catalysis.