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 turnover-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.