Effects of Attractive Through Space π-π* Interactions on the Structure, Reactivity, and Activity of Grubbs II Complexes

On the basis of theoretical calculations, the present work suggests that Grubbs II-type complexes are stabilized by a weak pi-pi* interaction involving an electronic donation from the aryl group of the NHC ligand to the pi* (Ru=C) molecular orbital, which is mainly centered on the carbenic carbon center (p(z) atomic orbital). This interaction, which could persist in the active catalytic species throughout a metathesis reaction, can be tuned by modulating the electron density in the aryl group.