The mechanism of inter-ring haptotropic rearrangements (IRHR) was investigated by DFT for tricarbonyl η 6 -complexes of group 6 metals (M = Cr, Mo, W) of coronene (I-M), kekulene (II-M) and a model graphene (III-M). The computed η 6 ,η 6 -IRHR activation barriers in the middle size PAHs I-M, and II-M were calculated to be substantially lower than in the case of complexes of relatively small size PAHs such as naphthalene chromium tricarbonyl (ΔG # ≈ 20-25 kcal mol -1 vs. ≈ 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 ).

International audienceA quantum chemical study of the mechanism and determination of the activation barriers of intramolecular eta(6),eta(6)-inner-ring haptotropic rearrangements (IHR), consisting in moving a chromium tricarbonyl group Cr(CO)(3) from one six-membered aromatic ring to another, are carried out using the density functional theory (DFT) for the respective eta(6)-complexes of coronene I and kekulene II. The stationary states on the potential energy surface, determining the mechanism of eta(6),eta(6)-IHR, have a lower hapticity, which is of interest for catalysis because of the possibility of coordinating an additional substrate and reagent around the transition metal during the rearrangement. The processes of eta(6),eta(6)-IHR complexes I and II occur with similar energy barriers (Delta G(not equal) ae 20-25 kcal/mol) that are lower than the barriers (Delta G(not equal) ae 30 kcal/mol) of similar transformations previously calculated or measured for naphthalene complexes and a number of small polyaromatic hydrocarbons

Metalcyclopentadienyl complexes (MCp)+ (M = Fe, Ru, Os) bound to the large polyaromatic hydrogenated hydrocarbon (PAH) C96H24 used as a model for pristine graphene have been studied using a density functional theory (DFT) generalized gradient approximation (PBE functional) to reveal their structural features and dynamic behavior. The inter-ring haptotropic rearrangements (IRHRs) for these complexes were shown to occur via two transition states and one intermediate. The energy barriers of the η6 ⇌ η6 IRHRs of the (MCp)+ unit were found to be 30, 27, and 29 kcal/mol for M = Fe, Ru, and Os, respectively. These values are significantly lower than the values found previously for smaller PAHs. Both polar and nonpolar solvents were found not to affect significantly the energy barrier heights. Investigated transition metal complexes could be used in general as catalysts in the design of novel derivatives or materials with promising properties. Metalcyclopentadienyl complexes (MCp)+ of PAHs show catalytic properties mainly due to their structural details as well as their important characteristic of inter-ring haptotropic rearrangement. IRHRs take place usually by intramolecular mechanisms. During IRHRs, the ML n organometallic groups (OMGs) undergo shifting along the PAH plane and could coordinate additional reagents, which is important for catalysis. Large PAHs such as graphene, fullerenes, and nanotubes possess intrinsic anticancer activity, and numerous arene complexes of Ru and Os have been proven to have anticancer properties as well. We suppose that coordinating Ru or Os to very large PAHs could synergistically increase the anticancer activity of resulting complexes.