Half-sandwich ruthenium(II) and rhodium(III) complexes bearing chiral amino-phosphoramidite ligands: Synthesis, characterization and application in asymmetric transfer hydrogenation of acetophenone

摘要

Cationic (η ~6-p-cymene) ruthenium(II) and (η ~5-C _5Me _5) rhodium(III) complexes containing chiral chelate P,N ligands (1R,2R)-N ~1-(4,8-di-tert-butyl- 2,10-dimethoxydibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)-N ~1,N ~2-dialkylcyclohexane-1,2-diamine (alkyl = Me L1, Et L2) have been synthesized and characterized by multinuclear one- and two-dimensional NMR spectroscopy, conductivity measurements, mass spectroscopy and elemental analysis. In the case of the ruthenium complexes [Ru(η ~6-p-cymene) (κ-P,κ-N)-(L1-L2)Cl]SbF _6 1-2, the diastereomer having an S _(Ru) configuration was formed with a de ≥ 98%. For rhodium complexes [Rh(η ~5-C _5Me _5)(κ-P,κ- N)-(L1-L2)Cl]SbF _6 3-4, the stereoselectivity of the chelation process and the configurational stability of the complexes depend on the reaction conditions and N-substituent of amino nitrogen. Some of these complexes have been tested as precatalysts in the asymmetric transfer hydrogenation of acetophenone by propan-2-ol.