Non-redox reactivity of V(II) and Fe(II) formamidinates towards CO 2 resulting in the formation of novel M(II) carbamates.

Chemical fixation of CO is a powerful tool for the preparation of novel multinuclear metal complexes and functional materials. Particularly, the insertion of CO 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 CO and V(II) and Fe(II) complexes supported by ,'-bis(2,6-diisopropylphenyl)formamidinate ligands (DippF). The reactions proceeded with multiple insertions of CO into the M-N bonds leading to the isolation of three novel complexes: [(κ-DippFCO)(THF)V(μ-DippFCO)V(THF)], [(κ-DippFCO)Fe(μ-DippFCO)(μ-DippF)Fe(THF)] and [(κ-DippFCO)Fe(μ-DippFCO)Fe(κ-DippFH)], which were characterised using single-crystal X-ray diffraction, FTIR and Fe Mössbauer spectroscopy (for the diiron compounds). We provide the first well-documented studies of the CO 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 CO 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).