Synthesis of Fe III and Fe IV Cyanide Complexes Using Hypervalent Iodine Reagents as Cyano-Transfer One-Electron Oxidants.

We disclose a new reactivity mode for electrophilic cyano λ 3 -iodanes as group transfer one-electron oxidants to synthesize Fe III and Fe IV cyanide complexes. The inherent thermal instability of high-valent Fe IV compounds without π-donor ligands (such as oxido (O 2- ), imido (RN 2- ) or nitrido (N 3- )) makes their isolation and structural characterization a very challenging task. We report the synthesis of an Fe IV cyanide complex [(N 3 N')FeCN] (4) by two consecutive single electron transfer (SET) processes from Fe II precursor [(N 3 N')FeLi(THF)] (1) with cyanobenziodoxolone (CBX). The Fe IV complex can also be prepared by reaction of [(N 3 N')Fe III ] (3) with CBX. In contrast, the oxidation of Fe II with 1-cyano-3,3-dimethyl-3-(1H)-1,2-benziodoxole (CDBX) enables the preparation of Fe III cyanide complex [(N 3 N')Fe III (CN)(Li)(THF) 3 ] (2-Li THF ). Complexes 4 and 2-Li THF have been structurally characterized by single crystal X-ray diffraction and their electronic structure has been examined by Mössbauer, EPR spectroscopy, and computational analyses.