Metal-Mediated Organocatalysis in Water: Serendipitous Discovery of Aldol Reaction Catalyzed by the [Ru(bpy)2(nornicotine)2]2+ Complex

David Guzmán Ríos, Miguel A. Romero, José A. González-Delgado, Jesús F. Arteaga, Uwe Pischel, J. Org. Chem. 2022,

The [Ru(bpy)2(Nor)2]2+ complex (Nor = nornicotine) is an efficient catalyst for the aldol reaction of acetone with activated benzaldehydes in buffered aqueous solution. The metal plays the role of an activator for the nornicotine organocatalyst ligands. The resulting catalytic activity is potentiated by a factor of about 4.5 as compared to free nornicotine. Similar rate enhancements can be achieved by using Zn(II) cations as activator. The observations are rationalized with the reduced basicity of the pyrrolidine N in nornicotine, due to the enhanced electron withdrawal of the metal-complexed pyridyl moiety.