Stereoselective Transfer Semi‐Hydrogenation of Alkynes to E‐Olefins with N‐Heterocyclic Silylene–Manganese Catalysts

• Published in: Chemistry : a European journal Vol. 24; no. 19; pp. 4780 - 4784
• Main Authors: Zhou, Yu‐Peng, Mo, Zhenbo, Luecke, Marcel‐Philip, Driess, Matthias
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 03.04.2018
• Subjects: Alkenes; Alkynes; Ammonia; Catalysts; Catalytic converters; Chemical synthesis; Chemistry; Coordination compounds; E-olefins; Functional groups; Hydrogen storage; Ligands; Manganese; N-heterocyclic silylene; Nitrogen dioxide; Pyridines; stereoselective catalysis; Substrates; transfer semi-hydrogenation; N-heterocyclic silylene; transfer semi-hydrogenation; E-olefins; manganese; stereoselective catalysis
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.201705745

The synthesis and structures of the first SiII‐donor supported manganese(II) complexes [L1]MnCl2, [L2]MnCl2, and [L3]2MnCl2 are reported, bearing a pincer‐type bis(NHSi)‐pyridine ligand L1, bidentate bis(NHSi)‐ferrocene ligand L2, and two monodentate NHSi ligands L3 (NHSi = N‐heterocyclic silylene), respectively. They act as unprecedented very active and stereoselective Mn‐based precatalysts (1 mol % loading) in transfer semi‐hydrogenations of alkynes to give the corresponding E‐olefins using ammonia–borane as a convenient hydrogen source under mild reaction conditions. Complex [L1]MnCl2 shows the best catalytic performance with quantitative conversion rates and excellent E‐stereoselectivities (up to 98 %) for different alkyne substrates. Different types of functional groups can be tolerated, except CN, NH2, NO2, and OH groups at the phenyl group of 1‐phenyl substituted alkynes. Give me the E: The first N‐heterocyclic silylene (NHSi)–manganese(II) complexes have been synthesized and fully characterized. Among them, the [L1]MnCl2 complex, which bear bis‐NHSi pyridine pincer ligand L1, acts as a superior precatalysts in homogeneous transfer semi‐hydrogenation of alkynes, using ammonia‐borane as a convenient hydrogen source at mild reaction conditions ([Mn]=[L1]MnCl2).