Rapid Reversible C–H Bond Activation By Nickel In the Presence of C-F Bonds BACKGROUND: C-H Bond activation reactions target the conversion of inexpensive hydrocarbon precursors into value-added fine chemicals. Most research on C-H bond activation to date has utilized complexes of the 2nd and 3rd row transition elements. Our research focus is to overcome the thermodynamic and kinetic difficulties associated with the use of less costly Ni complexes for C-H bond activations. RESULTS: Although previously published DFT studies suggested that Ni(0) complexes should not be thermodynamically capable of C–H bond activation with fluorinated aromatics and should undergo selective C–F bond activation, we have found that a source of the reactive (PEt3)2Ni moiety, 1, undergoes rapid and reversible C–H bond oxidative addition with 1,2,4,5-tetraflourobenzene. The reversibiliy of the reaction is demonstrated by the change in ratios of isotopomers 2a and 2b with temperature when monodeuterated 1,2,4,5-tetrafluorobenzene is used (Johnson; S.A., Huff, C.W. Mustafa, F.; Saliba, M J. Am. Chem Soc. 2008, 130, 17278–17280). Current work is underway to utilize these reactions in the direct functionalization of C-H bonds using nickel complexes.