Characterization and Reactivity of Iron Triazametallacyclohexadiene Complexes: Toward Iron-Catalyzed Multicomponent...

The fate of the catalyst in attempted iron-catalyzed imidazole synthesis has been identified as an iron triazametallacyclohexadiene species. Experimental and computational data confirm an S = ³/₂ ground state and a localized π-system within the metallacycle of this complex. Synthetic studies establish a multistep, one-pot route from a relatively stable iron chloride precursor. Other experiments show formation of the triazametallacyclohexadiene is more complicated than insertion to a discrete iron imide intermediate. Investigation into the reactivity of this complex points to the formation of a four-membered intermediate species upon nitrile elimination, as supported by exchange reactivity and isolation of the organic moiety by protonolysis. This four-membered metallacycle represents a potentially powerful intermediate in multicomponent coupling reactions catalyzed by (β-diketiminato)iron complexes.