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

The
iron­(IV) nitrido complex PhB­(MesIm)3FeN reacts
with 1,3-cyclohexadiene to yield the iron­(II) pyrrolide complex PhB­(MesIm)3Fe­(η5-C4H4N) 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.

四价铁氮化物配合物（iron(IV) nitrido complex）PhB(MesIm)3Fe≡N与1,3-环己二烯反应，以高产率生成二价铁吡咯根配合物（iron(II) pyrrolide complex）PhB(MesIm)3Fe(η5-C4H4N)。该产物的生成机理被认为涉及依次进行的[4+1]环加成（[4+1] cycloaddition）与逆狄尔斯-阿尔德反应（retro Diels–Alder reaction）。令人意外的是，该配合物与1,4-环己二烯反应同样可得到相同的含铁产物，尽管产率显著更低。经电子结构计算佐证的所提出的反应机理，涉及从1,4-环己二烯中夺取氢原子以生成环己二烯基自由基。该自由基是底物异构化为1,3-环己二烯过程中的中间体，最终促成吡咯根产物的生成。