Stabilization of Low-Valent Iron(I) in a High-Valent Vanadium(V) Oxide Cluster

Low-valent iron centers are critical intermediates in chemical and bio-chemical processes. Herein, we show the first example of a low-valent Fe^I center stabilized in a high-valent polyoxometalate framework. Electrochemical studies show that the Fe^III-functionalized molecular vanadium(V) oxide (DMA)[Fe^IIIClV^V ₁₂O₃₂Cl]³⁻ (DMA=dimethylammonium) features two well-defined, reversible, iron-based electrochemical reductions which cleanly yield the Fe^I species (DMA)[Fe^IClV^V ₁₂O₃₂Cl]⁵⁻. Experimental and theoretical studies including electron paramagnetic resonance spectroscopy and density functional theory computations verify the formation of the Fe^I species. The study presents the first example for the seemingly paradoxical embedding of low-valent metal species in high-valent metal oxide anions and opens new avenues for reductive electron transfer catalysis by polyoxometalates.