Site-Isolated Redox Reactivity in a Trinuclear Iron Complex

Abstract

The symmetric, high-spin triiron complex (PhL)Fe3(thf)3 reacts with mild chemical oxidants (e.g., Ph3CX, I2) to afford an asymmetric core where one iron ion bears the halide ligand (PhL)Fe3X(L), and the hexadentate (PhL = MeC(CH2NPh-o-NPh)3) ligand has undergone significant rearrangement. In the absence of a suitable trapping ligand, the Cl and Br complexes form (µ-X)2 bridged structures of the type [(PhL)Fe3(µ-X)]2. In the trinuclear complexes, the halide-bearing iron site sits in approximate trigonal bipyramidal (tbp) geometry formed by two (PhL) anilides and an exogenous solvent molecule. The two distal iron ions reside in distorted square-planar sites featuring a short Fe–Fe separation at 2.301 Å, whereas the distance to the tbp site is substantially elongated (2.6–2.7 Å). Zero-field, 57Fe Mössbauer analysis reveals the diiron unit as the locus of oxidation while the tbp site bearing the halide ligand remains divalent. Magnetic data acquired for the series reveals the oxidized diiron unit comprises a strongly coupled S = 3/2 unit that is weakly ferromagnetically coupled to the high spin (S = 2) ferrous site, giving an overall S = 7/2 ground state for the trinuclear units.