Cover Picture: (Adv. Synth. Catal. 17/2012)
Abstract:The cover picture, provided by Qi‐Lin Zhou, shows the example of an exceptionally highly efficient chiral catalyst. The catalyst is a very stable dihydride iridium complex of a tridentate chiral spiro P‐N‐N ligand based on the 1,1′‐spirobiindane skeleton, which exhibits excellent enantioselectivity and extremely high turnover number (in excess of one million) for the hydrogenation of both aryl ketones and β‐aryl‐β‐keto esters. Although little is known about the mechanism of this iridiumcatalyzed carbonyl group hydrogenation reaction, a non‐classical metalligand bifunctional mechanism deserves to be recommended to interpret the high efficiency of this catalyst. With the help of KO‐t‐Bu and under an H2 atmosphere, the dihydride iridium complex is converted to a trihydride iridium complex. After combination of the substrate with the trihydride iridium complex, a cyclic six‐membered transition state is formed. The hydridic IrH and protic NH of the catalyst are simultaneously transferred to the carbonyloxygen double bond of the substrate, resulting in a chiral alcohol and a hydrido amido iridium complex. Finally, the hydrido amido iridium complex is hydrogenated with H2 to regenerate the trihydride iridium complex.
Document Type: Research Article
Publication date: 2012-11-26