This hypothesis was then tested on a model substrate 12 with a various combinations of different copper sources, ligands and arenediazonium salts (Table ). We were delighted to find that when 2,4,6-trimethylbenzene diazonium salt 4a was used, 12 could efficiently couple with the difluoromethylzinc reagent 2 under copper-catalyzed conditions, affording the desired alkyl difluoromethane product 13 at room temperature (entry 1). The use of a sterically hindered and electron-rich diazonium salt 4a was crucial to the success of this reaction (entry 2 to 5). We reason that the electron-rich and sterically hindered aryl rings stabilized the aryl radicals, thereby preventing other undesired pathways. It is worth noting that 4a could be easily synthesized from the corresponding aniline (ca. $0.3/g) on a decagram scale and be stored in a -20°C freezer for at least a month without noticeable decomposition. Tridentate nitrogen ligand, terpyridine L1, was found to be beneficial for this reaction, while other bidentate ligands such as bipyridine L3 or phenanthroline L4 was less efficient (entry 6 to 8). We a Reactions were conducted with 12 (0.1 mmol, 1.0 equiv.), diazonium salt (0.25 mmol, 2.5 equiv.), 1 (0.15 mmol, 1.5 equiv.) Cu(OTf)2 (20 mol%), and ligand (20 mol%) in DMSO (0.6 mL) at R.T. b Yields were determined by F NMR using 1fluoro-3-nitrobenzene as the internal standard. c Conversion of 12, determined by GC using 1-fluoro-3-nitrobenzene as the internal standard. N.D., not detected.