Assessing Structure and Dynamics of Iron Complexes Supported by Tris(amidate)amine Ligands

Chelating ligand platforms derived from tris(2-aminoethyl)amine (TREN) can facilitate low coordination numbers and provide opportunities to tune the steric and electronic profile of the secondary coordination sphere. Herein, we examine the ability of two related tris(amidate)amine ligands to stabilize low-coordinate complexes of trivalent iron, and further use molecular dynamics (MD) simulations to gain insight into the dynamics of both the primary and secondary coordination spheres. Our cavitand-inspired ligand allows for the isolation of four-coordinate FeLOCH2O via oxidation of the anionic ferrous precursor, yielding the first crystallographically characterized example of an iron(III) species in a trigonal monopyramidal geometry. While this discovery is enabled by the rigid macrocycle in the secondary coordination sphere, MD simulations suggest that this macrocycle negligibly alters dynamics in the primary coordination sphere, and suggests a route by which exogenous ligands may bypass the rigid cavity opening yet still access the intracavity coordination site in [MLOCH2O]n complexes.