DFT Study on the Mechanisms of Iron-Catalyzed Ortho C–H Homoallylation of Aromatic Ketones with Methylenecyclopropanes

The mechanisms of iron-catalyzed ortho C–H homoallylation
of aromatic ketones with methylenecyclopropanes are calculated using
density functional theory calculations with B3LYP-D3BJ functionals
and solvation model density (cyclohexane) model. Our results show
that the catalytic cycle includes C–H bond oxidative addition,
insertion of C–C double bond, ring-opening reaction, reductive
elimination, ligand exchange, and the catalyst regeneration. Two possible
catalytic cycles are calculated, where Path A is where
the iron active catalyst first combined with 2,2-dimethyl-1-[4-(trifluoromethyl)
phenyl]-propan-1-one and Path B is where the iron active
catalyst initially attacked 2-phenyl-1-methylenecyclopropane. Our
calculated results show that the rate-determining step in the whole
catalytic cycle for the favored Path A is the C–H
bond oxidation addition step, where Gibbs free energy in solvent cyclohexane,
ΔGsol, is 10.8 kcal/mol.