Iron Catalyzed Double Bond Isomerization: Evidence for an Fe^I /Fe^III Catalytic Cycle

Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H₃ N⋅BH₃ ). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre-catalyst activation step that gives access to an η² -coordinated alkene Fe^I complex, followed by oxidative addition of the alkene to give an Fe^III intermediate, which then undergoes reductive elimination to allow release of the isomerization product.