Probing for Four-Coordinate Zerovalent Iron in a π-Acidic Ligand Field: A Functional Source of FeL4 Enabled by Labile Dinitrogen Binding

It has long been recognized that the first intermediate in chemical reactions mediated by Fe(CO) 5 is Fe(CO) 4 . However, the extreme instability of this unsaturated, high-spin species has hampered detailed structural and stoichiometric reactivity studies. The previously reported heteroleptic complex Fe(N 2 )(CO) 2 (CNAr Tripp2 ) 2 (Ar Tripp2 = 2,6-(2,4,6-( i -Pr) 3 C 6 H 2 ) 2 C 6 H 3 ), which is isolobal to Fe(CO) 5, is shown here to possess a labile dinitrogen ligand that allows it to perform reactions analogous to Fe(CO) 4 . Specifically, Fe(N 2 )(CO) 2 (CNAr Tripp2 ) 2 oxidatively adds dihydrogen, white phosphorus, and the Si–H bonds of triethylsilane and phenylsilane readily at room temperature and also binds tetrahydrofuran in the absence of N 2 . Accordingly, Fe(N 2 )(CO) 2 (CNAr Tripp2 ) 2 effectively serves as a masked form of Fe(CO) 4, allowing for well-defined reactivity and structurally characterizable reaction products.