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).