DFT study on the mechanism and structural aspects of iron(II)-catalyzed condensation of epichlorohydrin and CO2

Abstract

In this work, the catalytic cycle for the epichlorohydrin/CO₂ condensation using the [η⁵-(C₅H₅)Fe(CO)(L)]X complexes where L = NH₂(CH₂)₂PPh₂ and X = I (1), Br (2), Cl (3), OTf (4) and X = Br and L = NMe₂(CH₂)₂PPh₂ (7), NH₂(CH₂)₃PPh₂ (8), Py(CH₂)PPh₂ (9) and Py(PPh₂) (10), was studied computationally using density functional theory (DFT) at the ωB97xD/def2-TZVP level of theory. A good correlation between the optimized structures of complexes 1–4 and their respective X-ray diffraction (XRD) structures (used as experimental parameter) was found. Thus, the theoretical model was validated to study all the structures in the present work. The most thermodynamically and kinetically favored path for complexes 1–4 and 8, bearing acid hydrogens, operates outside of the coordination sphere as an ionic pathway where the ionic intermediates are stabilized through hydrogen bonds. Catalyst 2 showed the most favored energy profile among complexes 1–4 at room temperature and at 80 °C, which supports the previously reported experimental results. This first computational approach also explains the catalytic activity of complexes 1, 3 and 4. The most thermodynamically and kinetically favored path for complexes 7, 9, and 10 was the covalent pathway which works in the inner sphere, with a metal-alkoxide and a metal-carbonate as intermediates. Computationally, catalyst 10 was the most active catalyst in the entire study, showing a completely spontaneous energy profile at room temperature, being of great relevance to be investigated experimentally. Finally, the chiral R- and S-[η⁵-(C₅H₅)Fe(CO)(H(Me)N(CH₂)₂PPh₂)]Br isomers, computationally built and optimized from complex 2, were found to be highly favored stable isomers, also attractive for experimental research.