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 (eta(1) and eta(2)) 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 [(PtL3)-L-II(C6H6)] model complexes reveal a preference for the eta(2) mode, while the eta(1) 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 eta(1) arene complexes with benzonium cations shows that in the former case the bonding to the metal involves essentially the pi system of the arene, affecting only slightly the delocalized nature of the carboncarbon bonds. This behavior is in sharp contrast with the frequently found eta(1) coordination of Cp that involves sigma bonding and full dearomatization of the ring.