New C2-Symmetric Chiral Tetraaza Ligands and Their Application for [Ru(p-cymene)Cl₂]₂-Catalyzed Asymmetric Transfer Hydrogenation

Abstract

Two new chiral ligands (S, S, S, S)-N, N′-bis(2-p-toluene- sulfonylaminocyclohexyl) ethylenediamine (2a) and (S, S, S, S)-N, N′-bis(2-p-toluenesulfonylaminocyclohexyl) trimethylenediamine (2b) were prepared and confirmed by means of elemental analysis, IR, ¹H NMR, and MS. The catalytic effect for asymmetric transfer hydrogenation of acetophenone has been investigated using [Ru(p-cymene)Cl₂]₂ and above C2-symmetric chiral tetraaza ligands in 2-propanol/KOH. The chiral 1-phenylethanol was obtained with good conversion (87–98%) and low enantiometric excess (4–27%).

Keywords:

• acetophene
• asymmetric transfer hydrogenation
• chiral tetraaza ligands
• [Ru(p-cymene)Cl₂]₂

Acknowledgments

The authors express their gratitude to the Zhejiang Provincial Natural Science Foundation of China for financial Support through Project No. Y4090056.