The mechanism of inter-ring haptotropic rearrangements (IRHRs) was investigated by DFT for the tricarbonyl η⁶-complexes of group 6 metals (M = Cr, Mo, W) of coronene (I-M), kekulene (II-M) and a model graphene (III-M). The computed η⁶,η⁶-IRHR activation barriers in the middle size PAHs I-M and II-M were calculated to be substantially lower than those in the case of complexes of relatively small size PAHs such as naphthalene chromium tricarbonyl (ΔG^# ≈ 20–25 kcal mol⁻¹vs. ≈ 30 kcal mol⁻¹). The barrier is further lowered in the case of the model graphene complex III-Cr (ΔG^# ≈ 13 kcal mol⁻¹). An even lower barrier is found for III-Mo (ΔG^# ≈ 10 kcal mol⁻¹), whereas it slightly increases for III-W (ΔG^# ≈ 14 kcal mol⁻¹).