Exploring the Coordination of π-Acids and Redox-Active Diatomics to a High-Spin and Highly Fluorinated Ferrous Compound

A new trigonally symmetric ligand scaffold is reported from the reaction of tris(2-aminoethyl)amine (TREN) and methyl trifluoroacetate. Deprotonation and metallation with iron(II) yields a trigonal monopyramidal ferrate that bears an open coordination site surrounded by C–F motifs. The weak-field ligand environment promoted by the fluorinated amidate donors leads to distinctive behaviors that are apparent in reactions with π-acids such as CO and tert-butylisocyanide. As shown by structural, spectroscopic, and computational studies, the trifluoromethyl substituents lead to an attenuation of π-backbonding capabilities, while also labilizing the Fe–Namidate bonds. While no tractable reactivity with O2 occurs, the ferrate irreversibly coordinates NO to yield a high-spin {FeNO}7 complex.