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

Abstract

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