Nickel-Catalyzed Sonogashira Coupling Reactions of Nonactivated Alkyl Chlorides under Mild Conditions

The two nickel chlorides 1 and 2 with [P,S] and [P,Se] bidentate ligands, respectively, were synthesized and used as catalysts for Sonogashira coupling reaction. Both 1 and 2 are efficient catalysts for Sonogashira C­(sp3)–C­(sp) coupling reactions. Complex 1 has better catalytic activity than complex 2. In a combination of 1 mol % catalyst loading of 1 and CuI/Cs2CO3/DMSO at 25°C for the coupling reactions of alkyl iodides with terminal alkynes, the corresponding coupling products were obtained in moderate to excellent yields. This catalytic system is also suitable for alkyl bromides at 40 °C. It must be pointed out that with NaI as an additive complex 1 could effectively catalyze the C­(sp3)–C­(sp) coupling of nonactivated alkyl chlorides with alkynes under mild conditions (50 °C) with low catalyst loading (1 mol %). Complex 1 is easy to synthesize and has efficient catalytic activity, especially for alkyl chlorides, under mild conditions.