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

Abstract Cationic (η 6 - p -cymene) ruthenium(II) and (η 5 -C 5 Me 5 ) rhodium(III) complexes containing chiral chelate P,N ligands (1 R ,2 R )- 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 5 Me 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.