Site-Isolated Redox Reactivity in a Trinuclear Iron Complex

The symmetric, high-spin triiron complex (PhL)­Fe3(THF)3 reacts with mild chemical oxidants
(e.g.,
Ph3C-X, I2) to afford an asymmetric core, where
one iron 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 chlorine and bromine
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 atoms 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 reveal that 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.