Prof. Qiang Liu; Tsinghua University
When: Wednesday, October 23, 2024, 5:15 pm
Where: TUM Department of Chemistry, Science Cinema (Hörsaal CH 26411)
Title: Anionic Mn-Hydride Complexes—Reactivity and Catalysis
The reduction of polar unsaturated bonds is a fundamental and important transformation. Common reducing agents include reactive metal hydrides such as LiAlH₄ and NaBH₄. Metal hydride reducing agents like LiAlH₄ are typical anionic metal-hydride complexes, where the AlH₄⁻ anion has a strong hydride nucleophilicity. The Li⁺ cation serves as a counterion and can coordinate with the more electronegative heteroatoms in polar bonds, effectively enhancing the electrophilicity of the substrate. The above two beneficial effects lead to excellent reducing reactivity. However, such reagents are usually utilized in stoichiometric amounts and generate large quantities of metal salt by-products, which do not align with the principles of green chemistry. Hydrogen gas, as a reducing agent, offers advantages such as low cost and high atom economy. The key to realize catalytic hydrogenation is the efficient formation and conversion of transition metal hydride intermediates. However, these intermediates are typically neutral complexes, and their hydride transfer reactivity and reduction capability are generally lower than that of anionic metal hydrides like LiAlH₄. To address this, we have developed an anionic manganese hydride catalytic system with high hydride nucleophilicity. The counter metal cation not only activates the substrate through coordination but also effectively stabilizes key reaction intermediates and favorable transition states. Additionally, it exhibits an enzyme-like chiral induction mode, enabling highly efficient and selective catalytic hydrogenation reactions.