Oxidation of Iron Complex with NHC Ligand with Molecular Iodine

Abstract

Complex (η⁵-C₅H₅)₂Fe₂(CO)₄ (I) reacts with 1,3-dimethylimidazolium-2-carboxylate Me₂ImCO₂ to give asymmetric binuclear carbene iron complex (η⁵-C₅H₅)₂Fe₂(CO)₃(Me₂Im) (II) (Me₂Im = 1,3-dimethylimidazol-2-ylidene). The oxidation of compound II with elemental iodine proceeds via two mechanisms, symmetrical and asymmetrical, to form four products: (η⁵-C₅H₅Fe(CO)₂(Me₂Im)I (III), (η⁵-C₅H₅)Fe(CO)₂I (IV), (η⁵-C₅H₅Fe(CO)₂(Me₂Im)I₃ (V), and ferrocene (VI). In each case, two pairs of reaction products have formed, two of which include NHC ligand: neutral iron(III) complex and ionic complex V. Optimal synthesis conditions to obtain preferably one of these complexes have been found. Geometry and transition state energy of supposed reaction mechanism have been calculated by quantum chemistry methods.