Non-redox reactivity of V(ii) and Fe(ii) formamidinates towards CO2 resulting in the formation of novel M(ii) carbamates

Abstract

Chemical fixation of CO₂ is a powerful tool for the preparation of novel multinuclear metal complexes and functional materials. Particularly, the insertion of CO₂ into a metal–X bond (X = H, C, N, O) often is a key elementary step in the various processes transforming this greenhouse gas into valuable products. Herein, we report on the reactivity between CO₂ and V(II) and Fe(II) complexes supported by N,N′-bis(2,6-diisopropylphenyl)formamidinate ligands (DippF). The reactions proceeded with multiple insertions of CO₂ into the M–N bonds leading to the isolation of three novel complexes: [(κ²-DippFCO₂)(THF)V(μ-DippFCO₂)₃V(THF)], [(κ²-DippFCO₂)Fe(μ-DippFCO₂)₂(μ-DippF)Fe(THF)] and [(κ²-DippFCO₂)Fe(μ-DippFCO₂)₃Fe(κ¹-DippFH)], which were characterised using single-crystal X-ray diffraction, FTIR and ⁵⁷Fe Mössbauer spectroscopy (for the diiron compounds). We provide the first well-documented studies of the CO₂ reactivity towards the V–N bond and broaden the state-of-the-art of the undeveloped area of the reactivity of low-valent V(II) complexes. Moreover, we showed that the effectivity of the examined CO₂ insertion processes strongly depends on the used solvent's characteristics (for the Fe(II) system) and the metal centre's coordination sphere geometry (for the V(II) system).