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 FeL^OCH2Ovia oxidation of the anionic and isostructural ferrous precursor, demonstrating how the secondary sphere macrocycle can promote the retention of an open coordination site. Through comparison with a non-macrocyclized tris(amidate)amine ligand, molecular dynamics (MD) simulations are used to garner insights into how this macrocycle alters coordination sphere dynamics. Additionally, both four-coordinate FeL^OCH2O and five-coordinate Fe(DMF)L^OMe are shown to be synthons for the trigonal bipyramidal ferric fluoride complexes [Fe(F)L^OCH2O]⁻ and [Fe(F)L^OMe]⁻, respectively.