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 2 is a powerful tool for the preparation of novel multinuclear metal complexes and functional materials. Particularly, the insertion of CO 2 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 2 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 CO 2 into the M-N bonds leading to the isolation of three novel complexes: [(κ 2 -DippFCO 2 )(THF)V(μ-DippFCO 2 ) 3 V(THF)], [(κ 2 -DippFCO 2 )Fe(μ-DippFCO 2 ) 2 (μ-DippF)Fe(THF)] and [(κ 2 -DippFCO 2 )Fe(μ-DippFCO 2 ) 3 Fe(κ 1 -DippFH)], which were characterised using single-crystal X-ray diffraction, FTIR and 57 Fe Mössbauer spectroscopy (for the diiron compounds). We provide the first well-documented studies of the CO 2 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 2 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).