Isocyanide Substituent Influences Reductive Elimination versus Migratory Insertion in Reaction with an [Fe₂(μ-H)₂]²⁺ Complex

Iron hydrides are proposed reactive intermediates for N₂ and CO conversion in industrial and biological processes. Here, we report a reactivity study of a low-coordinate di(μ-hydrido)diiron(II) complex, Fe₂(μ-H)₂L, where L^2– is a bis(β-diketiminate) cyclophane, with isocyanides, which have electronic structures related to N₂ and CO. The reaction outcome is influenced by the isocyanide substituent, with 2,6-xylyl isocyanide leading to H₂ loss, to form a bis(μ-1,1-isocyanide)diiron(I) complex, whereas all of the other tested isocyanides insert into the Fe–H bond to give (μ-1,2-iminoformyl) complexes. Steric bulk of the isocyanide substituent determines the extent of insertion (i.e., into one or both Fe–H–Fe units) with tert-butyl isocyanide reacting to yield the mono-(μ-1,2-iminoformyl)diiron(II) complex, exclusively, and isopropyl- and methyl isocyanides affording the bis(μ-1,2-iminoformyl)diiron(II) products. Treatment of Fe₂(μ-1,2-CHNtBu)(μ-H)L with 2,6-xylyl isocyanide (or XylNC) yields Fe₂(μ-XylNC)₂L and tert-butylaldimine as one of the organic products.