Iridium-catalyzed asymmetric hydrogenation

作者：Valla C^*; Pfaltz A

来源：Chimica Oggi-Chemistry Today, 2004, 22(9): 4-7.

Cationic iridium complexes with chiral PN-ligands and tetrokis[3,5-bis(trifluoromethyl)phenyl]borate (BArF) as the counterion are efficient homogeneous catalysts for-the enantioselective hydrogenation of olefins. In contrast to chiral rhodium- and ruthenium-phosphine catalysts, they do not require the presence of a polar coordinating group near the C=C bond. In the hydrogenation a unfunctionalized aryl-substituted olefins, high enantioselectivities of > 95% ee with full conversion, turnover numbers of up to 5000 and turnover frequencies of >5000 h(-1) have been achieved. As illustrated by the examples given in Schemes 3 and 4, the application range is largely complementary to chiral Rh and Ru catalysts. Several types of functionalized and unfunctionalized olefins, for which no suitable catalysts were previously available, can now be hydrogenated with high efficiency and good to excellent enantioselectivity. The iridium complexes used as precatalysts are air-stable and easy to handle. Further attractive features are the ready availability and the modular nature of the chiral ligands, making it possible to optimize the catalyst structure for a specific substrate.

• 出版日期2004-9