Reaction of an Iron(IV) Nitrido Complex with Cyclohexadienes: Cycloaddition and Hydrogen-Atom Abstraction

[Image: see text] The iron(IV) nitrido complex PhB(MesIm)(3)Fe≡N reacts with 1,3-cyclohexadiene to yield the iron(II) pyrrolide complex PhB(MesIm)(3)Fe(η(5)-C(4)H(4)N) in high yield. The mechanism of product formation is proposed to involve sequential [4 + 1] cycloaddition and retro Diels–Alder reactions. Surprisingly, reaction with 1,4-cyclohexadiene yields the same iron-containing product, albeit in substantially lower yield. The proposed reaction mechanism, supported by electronic structure calculations, involves hydrogen-atom abstraction from 1,4-cyclohexadiene to provide the cyclohexadienyl radical. This radical is an intermediate in substrate isomerization to 1,3-cyclohexadiene, leading to formation of the pyrrolide product.