Room temperature Z-selective hydrogenation of alkynes by hemilabile and non-innocent (NNN)Co(ii) catalysts

Abstract

Hemilabile and phosphine-free quinolinyl-based NNN-type pincer and non-pincer cobalt complexes were developed for the room temperature catalytic transfer semi-hydrogenation of alkynes to Z-alkenes. Treatment of the quinolinyl-amine ligand, [C₉H₆N(NH)CH₂CH₂NEt₂] (^QNNN^CH₂NEt₂)–H with CoX₂ afforded the pincer complexes κ³-(^QNNN^CH₂NEt₂)CoX₂ (X = Cl, Br), whereas, the quinolinyl-amide ligand, [C₉H₆N(NH)C(O)CH₂NEt₂] (^QNNN^C(O)NEt₂)–H gave chelate anionic complexes κ²-(^QNN)CoX₂(N^C(O)HNEt₂) (X = Cl, Br). The well-defined anionic non-pincer cobalt complexes efficiently catalyzed the semi-hydrogenation of diverse alkynes to deliver highly chemoselective and stereodivergent Z-alkenes at room temperature. This hydrogenation exhibited broad substrate scope with the tolerance of sensitive functional groups, such as –Cl, –Br, –I, –OH, –NH₂, –COOMe, and pyridinyl, employing a stable and user-friendly ammonia borane hydrogen source.