Mechanistic Insights into the Phosphine-Free RuCp*-Diamine-Catalyzed Hydrogenation of Aryl Ketones: Experimental and Theoretical Evidence for an Alcohol-Mediated Dihydrogen Activation

作者：Christian Hedberg, Klas Källström, Per I. Arvidsson, Peter Brandt, Pher G. Andersson · 发表于：Journal of the American Chemical Society · 年份：2005 · DOI：10.1021/ja051920q · 被引用次数：144 · 研究领域：Asymmetric Hydrogenation and Catalysis、Surface Chemistry and Catalysis、Chemical Synthesis and Analysis

The commercially available chiral diamine quincorine-amine, originally derived from quinine, was found to be a highly active catalyst for ruthenium-catalyzed hydrogenation of ketones. The complex formed between the quincorine-amine, containing both a primary and a quinuclidine amino function, and RuCp*Cl catalyzes the hydrogenation of aromatic and aliphatic ketones in up to 90% ee approximately 24 times faster than previously reported Ru-diamine complexes. The pseudo-enantiomer of the quincorine-amine, i.e., quincoridine-amine, also showed high activity; however, the enantioselectivities obtained with this catalyst were lower. The reason for the lower, but opposite stereoselectivity seen with the quincoridine-amine, as compared to the quincorine-amine, was rationalized by a kinetic and computational study of the mechanism of the reaction. The theoretical calculations also revealed a significantly lower activation barrier for the alcohol-mediated split of dihydrogen, as compared to the nonalcohol-mediated process, a finding of utmost implication also for the diphosphine/diamine-mediated enantioselective hydrogenation of ketones.