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

Iron hydrides are proposed reactive intermediates for N and CO conversion in industrial and biological processes. Here, we report a reactivity study of a low-coordinate di(μ-hydrido)diiron(II) complex, Fe(μ-H), where is a bis(β-diketiminate) cyclophane, with isocyanides, which have electronic structures related to N and CO. The reaction outcome is influenced by the isocyanide substituent, with 2,6-xylyl isocyanide leading to H 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 -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 Fe(μ-1,2-CHNtBu)(μ-H) with 2,6-xylyl isocyanide (or XylNC) yields Fe(μ-XylNC) and -butylaldimine as one of the organic products.