Achieving a Favorable Activation of the C–F Bond over the C–H Bond in Five- and Six-Membered Ring Complexes by a Coordination and Aromaticity Dually Driven Strategy
Activating the C–F bond (the strongest σ bond to carbon) is particularly challenging, let alone in a selective fashion when a weaker C–H bond is present in the same species. Herein, we demonstrate a novel strategy to achieve a thermodynamically and kinetically favorable activation of the C–F bond over the C–H bond dually driven by coordination and aromaticity via density functional theory calculations. Specifically, the bond dissociation energies (BDEs) of the C–H bond in 5-fluoro-1,2,3,4-tetramethylcyclopenta-1,3-diene increase remarkably after its coordination to the metal centers (Co, Rh, and Ir), whereas the BDE changes in the C–F bond of Rh and Ir complexes are insignificant. The C–F bond activation of the Co system has the lowest energy barrier and the largest exergonicity due to significant weakening of the C–F bond of reactants after coordination. Aromaticity is found to play an important role in stabilizing the transition states and products during the reactions, which is indicated by gradually increased multicenter index values along the intrinsic reaction coordinate. In addition, stronger electrostatic attraction in the transition states between the metal center and F over the H atom could be another factor for the lower reaction barrier of the C–F bond activation. All these findings provide a fundamental understanding of competitive activation of the C–F and C–H bonds, inviting experimental chemists’ verification.