γ-Agostic interactions in ( Mes CCC)Fe-Mes(L) complexes.

Agostic interactions were observed in the bound mesityl group in a series of iron compounds bearing a bis(NHC) pincer CCC ligand. The L-type ligand on [(CCC)Fe II Mes(L)] complexes influences the strength of the agostic interaction and is manifested in the upfield shift of the 1 H NMR resonance for the mesityl methyl resonances. The nature of the interaction was further investigated by density functional theory calculations, allowing rationalization of some unexpected trends and proving to be a powerful predictive tool.