Z-Selective Semihydrogenation of Electron-Deficient Alkynes Using Cu(dppf)(BH4) as the Hydrogen Donor

Abstract

Semihydrogenation of alkynes to (Z)- or (E)-alkenes is a crucial process for producing structural units in natural products, pharmaceuticals, and agrochemicals. Although various catalytic systems have been developed for cost-effective and environmentally friendly alkyne semihydrogenation, high-performance catalysts for the semihydrogenation of electron-deficient alkynes remain rare. Herein, an efficient Z-selective transfer semihydrogenation of electron-deficient alkynes in alkyl amides was developed under mild conditions (70 °C, atmospheric pressure) from a heteroatom binuclear material, Cu(dppf)(BH₄). Control experiments, kinetic studies, deuterium-labeling experiments with Cu(dppf)(BD₄), and DFT calculations suggest that Cu(dppf)(BH₄) transfers a hydride to the electron-rich alkyne carbon, followed by protonation in a cis fashion. The significant role of each functional unit in Cu(dppf)(BH₄) is underlined herein. This development will pave the way for new opportunities for the creation of efficient metal borohydrides for reduction reactions and new hydrogen storage materials.