New Copper and Rhodium Cyclopropanation Catalysts Supported by Chiral Bis(pyrazolyl)pyridines. A Metal-Dependent Enantioselectivity Switch

Copper and rhodium complexes of new optically pure bis(pyrazolyl)pyridines catalyze the cyclopropanation of styrene with moderate to high enantioselectivities, but the sense of asymmetric induction observed depends on the nature of the metal ion, implicating interesting mechanistic differences between the copper- and rhodium-based systems.