Our optimization experiments (Table ) suggested that the reaction proceeds via the cleavage of benzylic C(sp 3 )-F bonds followed by homobenzylic bond cleavage. An analysis of the reaction mixture via periodic sampling revealed that 2 and 5 are initially formed and ultimately consumed, whereas the concentrations of 3 and 4 continue to increase (Figure ). This result suggests that 2 and 5 are reaction intermediates to produce 3. Especially 2 is a reasonable reaction intermediate given that our previous work suggests that the coordination of Ni(0) to a trifluoromethyl arene leads to the oxidative addition of a proximal benzylic C(sp 3 )-F bond. We then investigated the effect of the base on the benzylic C-F bond cleavage process. We periodically analyzed reaction mixtures containing 0.2 M of 1a, a catalytic amount of Ni(0) and ICy, and a tenfold excess of PhMe2SiH with or without K3PO4. The initial reaction rates kobs (~25% conversion) were obtained by plotting the concentration (mM) of 1a as a function of time (min) (Figure ). When we performed the reaction without K3PO4, the reaction rate was not influenced. This result indicates that the base does not participate in the rate-determining step at this stage. We then measured kobs for different Ni/ICy ratios using Ni(cod)2 and ICy (Figure ). When the ratio Ni/ICy was greater than 2, the reaction rate was proportional to the amount of ICy. In contrast, when more than two equivalents of ICy were added relative to Ni, the reaction slowed down.