Ruthenium-catalyzed reactions for organic synthesis

Organic syntheses promoted by ruthenium catalysts are reviewed. Since ruthenium has 4d75s1 electron configuration, it has the widest scope of oxidation states (from -2 valent in Ru(CO)4 2- to octavalent in RuO4) of all elements of the periodic table, and various coordination geometries in each electron configuration, which is in contrast to the narrow scope of oxidation states and simple square planar structure of palladium. A number of homogeneous and heterogeneous ruthenium complexes catalyze hydrogenation of various substrates including functionalized olefins, aldehydes, ketones, other carbonyl compounds, and nitro compounds. Great progress has been made on the asymmetric hydrogenations with homogeneous ruthenium complexes bearing chiral phosphine ligands. The chiral diamine-ruthenium complexes also catalyze asymmetric reduction of imines with a formic acid-triethylamine mixture. This method is useful for asymmetric reduction of cyclic imines, providing a general and convenient route to a various indole alkaloids.