Isolation and Reactivity of an Iron Azametallacyclobutene Complex

A variety of C-N bond-forming methods are enabled by the [2 + 2] cycloaddition reaction of a transition metal imide complex and an alkyne substrate to generate an azametallacyclobutene intermediate. This type of reactivity has been primarily limited to early transition metals like zirconium and titanium. Herein, we describe the preparation of an iron azametallacyclobutene complex by [2 + 2] cycloaddition of a beta- diketiminate iron imide complex and an internal alkyne, 1-phenyl-1-propyne. The metallacycle reacts further upon exposure to a terminal alkyne, phenylacetylene, by a proposed protonation pathway that is distinct from the chemistry of its group 4 congeners and is in line with formation of an azametallacyclobu-tene intermediate in iron-catalyzed alkyne carboamination. The iron azametallacyclobutene complex also undergoes migratory insertion of aldehyde and nitrile substrates to the metal-nitrogen bond, in contrast to the exclusive metal-carbon insertion that has been observed for zirconium and titanium analogs.