Key points are not available for this paper at this time.
Aryl triflates make up a class of aryl electrophiles that are available in a single step from the corresponding phenol. Despite the known reactivity of nickel complexes for aryl C–O bond activation of phenol derivatives, nickel-catalyzed cross-electrophile coupling using aryl triflates has proven challenging. Herein, we report a method to form C(sp 2 )–C(sp 3 ) bonds by coupling aryl triflates with alkyl bromides and chlorides using phenanthroline (phen) or pyridine-2,6-bis( N -cyanocarboxamidine) (PyBCam CN )-ligated nickel catalysts. The scope of the reaction is demonstrated with 38 examples (61 ± 14% average yield). Mechanistic studies provide a rationale for the conditions used and a roadmap for further applications of cross-electrophile coupling. First, the rate of alkyl radical generation is controlled by maintaining the majority of alkyl halide as the alkyl chloride, which is unreactive, and utilizing a dynamic halide exchange process to adjust the concentration of reactive alkyl bromide or iodide. Second, the challenge of using electron-rich aryl triflates appears to be due to off-cycle transmetalation to form unproductive aryl zinc reagents. The optimal PyBCam CN ligand together with LiCl avoids this deleterious transmetalation step.
Kim et al. (Fri,) studied this question.