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

Abstract

The synthesis and structures of the first Si^II -donor supported manganese(II) complexes [L1]MnCl₂ , [L2]MnCl₂ , and [L3]₂ MnCl₂ 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.

Keywords: E-olefins; N-heterocyclic silylene; manganese; stereoselective catalysis; transfer semi-hydrogenation.