The role of Cr, Mo and W in the electronic delocalization and the metal-ring interaction in metallocene complexes

Metal influence over triple-decker, sandwich-like and pyramidal structured benzenes was studied by means of Energy Decomposition Analysis (Morokuma-Ziegler), combined with Extended Transition State Natural Orbitals for Chemical Valence, finding that metal-ring bonding was a covalent contribution of about 60% due to the bonding interaction between d_xz and d_yz, d_x²-y² and d_xy orbitals with p_z orbitals, respectively, adapted by symmetry in the ring, to form π and δ bonding interactions. Finally, an important amount of electron density between the ring and the metal was found. This has a key role in the electron delocalization in this zone. This electronic delocalization was analysed via Induced Magnetic Field and Nucleus-Independent Chemical Shift calculations, finding a pattern between metal atomic radii and shielding tensor. Furthermore, similar behaviour for Mo and W, in the enhancement of the diatropic magnetic response, was displayed while Cr had a slightly lower diatropic character.