Nickel-Catalyzed Direct Alkylation of Terminal Alkynes at Room Temperature: A Hemilabile Pincer Ligand Enhances Catalytic Activity
Direct coupling of alkyl halides with terminal alkynes provides an efficient and streamlined access to alkyl-substituted alkynes, which are important synthetic intermediates, biologically active molecules, and organic materials. However, until now,there have been fewer than a handful of catalytic methods available for this reaction, and detailed mechanistic studies have not been reported. Herein, we describe the design and development a new nickel pincer complex that catalyzes the direct coupling of primary alkyl halides with terminal alkynes at room temperature. The catalysis has a good substrate scope and high functional group tolerance. Kinetic data suggest that the new pincer ligand is hemilabile, and the dissociation of a labile amine donor is the (t)urnover-determining step of the catalysis. An intermediate Ni-alkynyl species has been isolated and structurally characterized. The reactivity of this species gives insight into the nature of the active species for the activation of alkyl halide.