Alkanes C1-C6 C-H Bond Activation via a Barrierless Potential Energy Path: Trifluoromethyl Carbenes Enhance Primary C-H Bond Functionalization

In this mixed computational and experimental study, we report a catalytic system for alkane C1-C6 functionalization in which the responsible step for C-H bond activation shows no barrier in the potential energy path. DFT modeling of three silver-based catalysts and four diazo compounds led to the conclusion that the TpFAg=C(H)CF3 (TpF = fluorinated trispyrazolylborate ligand) carbene intermediates interact with methane without a barrier in the potential energy surface, a prediction validated by experimentation using N2=C(H)CF3 as the carbene source. The array of alkanes from propane to n-hexane led to the preferential functionalization of the primary sites with unprecedented values of selectivity for an acceptor diazo compound. The lack of those barriers implies that selectivity can no longer be controlled by differences in the energy barriers. Molecular dynamics calculations (with propane as the model alkane) are consistent with the preferential functionalization of the primary sites due to a higher concentration of such C-H bonds in the vicinity of the carbenic carbon atom.