Electronic and structural effects of low-hapticity coordination of arene rings to transition metals

A DFT computational study and a structural analysis of the coordination of arenes to transition metals in low -hapticity (η1 and η2) modes have been developed, including a pseudosymmetry analysis of the molecular orbitals and the introduction of a hapticity map that makes evident the different degrees of intermediate hapticities. Calculations on [PtIIL3(C6H6)] model complexes reveal a preference for the η2 mode, while the η1 coordination is found to be a low-energy transition state for a haptotropic shift. The attachment of the arene to a side group that is coordinated to the metal introduces geometrical constraints, which result in hapticities intermediate between one and two. Comparison of the η1 arene complexes with benzonium cations shows that in the former case the bonding to the metal involves essentially the η system of the arene, affecting only slightly the delocalized nature of the carbon-carbon bonds. This behavior is in sharp contrast with the frequently found η1 coordination of Cp that involves σ bonding and full dearomatization of the ring. ; Peer reviewed