DFT Study of the Mechanisms of Iron-Catalyzed Regioselective Synthesis of α‑Aryl Carboxylic Acids from Styrene Derivatives and CO2

The mechanisms of highly regioselective iron­(II)-catalyzed synthesis of α-carboxylic acids from alkene derivatives and CO2 have been investigated using density functional theory (DFT) calculations at the B3LYP-D3 level. The results show that the overall catalytic cycle includes β-hydride elimination, hydrometalation, oxidative addition of EtMgBr, reductive elimination, and carboxylation using CO2. However, the first and second steps could be replaced by a favored concerted one-step mechanism without forming the iron hydride complex. The rate-limiting step for the whole catalytic cycle is the reductive elimination step, where the energy barrier ΔE is 37.3 kcal/mol in the gas phase and the Gibbs free energy in solvent THF ΔGsol is 30.3 kcal/mol, computed using the SMD method. The mechanisms to obtain the byproduct β-carboxylic acids are also studied.