Room temperature Z-selective hydrogenation of alkynes by hemilabile and non-innocent (NNN)Co(ii) catalysts†
bc
and
Benudhar
Punji
*ab
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] (QNNNCH2NEt2)–H with CoX2 afforded the pincer complexes κ3-(QNNNCH2NEt2)CoX2 (X = Cl, Br), whereas, the quinolinyl-amide ligand, [C9H6N(NH)C(O)CH2NEt2] (QNNNC(O)NEt2)–H gave chelate anionic complexes κ2-(QNN)CoX2(NC(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.
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