Arene Insertion into the M–Cl Bond vs Addition-like Behavior of Arene and M–Cl Bond (M = Cu/Fe): A DFT Investigation of the Cu/Fe SET Mechanism of Arene sp² C–H Chlorination

MClx-catalyzed (MClx = CuCl2/FeCl3) arene sp2 C–H chlorination was calculated at the DKH//B3LYP-D3//DKH-def2-TZVP level in solvent. The mechanism consists of two competing paths: (i) the arene insertion path into the M–Cl bond and (ii) the M–Cl addition-like path onto the arene ring. The latter path has fewer steps and lower activation energies. In both paths, one M–Cl bond breaks at the first step and then the valence state stays at Cu(I)/Fe(II) for the main part of the following steps. Cu exhibits better catalytic performance due to its lesser bonding capability. Weak M–H interactions were observed in the insertion mechanism.