Sandoval Christian A, Li Yuehui, Ding Kuiling, Noyori Ryoji
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai, China.
Chem Asian J. 2008 Oct 6;3(10):1801-10. doi: 10.1002/asia.200800246.
Chiral binap/pica-Ru(II) complexes (binap=(S)- or (R)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl; pica=alpha-picolylamine) catalyze both asymmetric hydrogenation (AH) of ketones using H(2) and asymmetric transfer hydrogenation (ATH) using non-tertiary alcohols under basic conditions. The AH and ATH catalytic cycles are linked by the metal-ligand bifunctional mechanism. Asymmetric reduction of pinacolone is best achieved in ethanol containing the Ru catalyst and base under an H(2) atmosphere at ambient temperature, giving the chiral alcohol in 97-98 % ee. The reaction utilizes only H(2) as a hydride source with alcohol acting as a proton source. On the other hand, asymmetric reduction of acetophenone is attained with both H(2) (ambient temperature) and 2-propanol (>60 degrees C) with relatively low enantioselectivity. The degree of contribution of the AH and ATH cycles is highly dependent on the ketone substrates, solvent, and reaction parameters (H(2) pressure, temperature, basicity, substrate concentration, H/D difference, etc.).
手性联萘二膦/吡啶甲基胺钌（II）配合物（联萘二膦=（S）-或（R）-2,2'-双（二苯基膦基）-1,1'-联萘；吡啶甲基胺=α-吡啶甲基胺）在碱性条件下既催化酮使用H₂的不对称氢化（AH），也催化使用非叔醇的不对称转移氢化（ATH）。AH和ATH催化循环通过金属-配体双功能机理相联系。在室温下的H₂气氛中，在含有钌催化剂和碱的乙醇中，频哪酮的不对称还原效果最佳，得到的手性醇对映体过量值为97-98%。该反应仅使用H₂作为氢化物源，醇作为质子源。另一方面，可以使用H₂（室温）和2-丙醇（>60℃）实现苯乙酮的不对称还原，但对映选择性相对较低。AH和ATH循环的贡献程度高度依赖于酮底物、溶剂和反应参数（H₂压力、温度、碱度、底物浓度、H/D差异等）。
