Sonogashira reactions of alkyl halides catalyzed by NHC [CNN] pincer nickel(ii) complexes

Abstract

C(carbene)N(amido)N(amine)-pincer nickel(II) complexes [^iPrCNN-Ni-Br] (6), [^nBuCNN-Ni-Br] (7) and [^BnCNN-Ni-Cl] (8) were synthesized. The catalytic performance of complexes 6–8 for Sonogashira cross-coupling reactions was explored. In a combination of 5 mol% catalyst loading of 6 and CuI/Cs₂CO₃/NaI/DMSO at different temperatures for the coupling reactions between alkyl iodides, bromides, chlorides and terminal alkynes, the corresponding coupling products were obtained in moderate to excellent yields. The mechanism of these catalytic reactions was discussed and partially supported by experiments. The phenylethynyl CNN pincer nickel complex 9 as a catalytically active complex was isolated and structurally characterized using X-ray diffraction.