Synthesis of FeIII and FeIV Cyanide Complexes Using Hypervalent Iodine Reagents as Cyano-Transfer One-Electron Oxidants

Abstract

We disclose a new reactivity mode for electrophilic cyano λ³ -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 [(N₃ N')FeCN] (4) by two consecutive single electron transfer (SET) processes from Fe^II precursor [(N₃ N')FeLi(THF)] (1) with cyanobenziodoxolone (CBX). The Fe^IV complex can also be prepared by reaction of [(N₃ 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 [(N₃ 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.

Keywords: Group-Transfer Reactions; Hypervalent Compounds; Iron; Iron(IV) Cyanide; Single-Electron Transfer.