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Synthesis, Characterization, and Reactivity of Iron(III) Complexes Supported by a Trianionic ONO3– Pincer Ligand

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posted on 15.12.2014, 00:00 by Matias E. Pascualini, Natali V. Di Russo, Pedro A. Quintero, Annaliese E. Thuijs, Dawid Pinkowicz, Khalil A. Abboud, Kim R. Dunbar, George Christou, Mark W. Meisel, Adam S. Veige
Synthetic and characterization results of a new family of Fe­(III) compounds stabilized by a trianionic [CF3–ONO]3– pincer-type ligand are reported. The ligand possesses three negatively charged donors constrained to the meridional positions that provide sufficient electron density to stabilize high-valent metal complexes. Using the redox-insulated [CF3–ONO]3–, pentacoordinated square-pyramidal {[CF3–ONO]­FeCl2}­{LiTHF2}2 (3), dimeric μ-DME­{[CF3–ONO]­FeDME}2 (4), trigonal bipyramidal [CF3–ONO]­Fe­(bpy) (5), and octahedral [CF3–ONO]­Fe­(bpy)­H2O (5·H2O) complexes are synthesized. An interesting feature of the [CF3–ONO]3– pincer-type ligand is its ability to coordinate the metal center in both the more common meridional positions or occupying a face of a trigonal bipyramidal complex. The molecular structure of 3 contains structural features similar to those of a rare square-planar high-spin Fe­(II) complex, and the important role of the counterions in stabilizing a square-plane is emphasized. SQUID magnetometry measurements of 3 reveal its high-spin character, and cyclic voltammetry measurements indicate high oxidation state species are unstable. However, all compounds can be reduced, and in particular 5 displays a reversible reduction event at −2255 mV versus ferrocene (Fc+/Fc) that can be assigned to either the FeI/Fe0 couple or 2,2′-bipyridine reduction.

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