Chiral Cyclopentadienyl Ruthenium Complexes as Versatile Catalysts for Enantioselective Transformations

Ruthenium complexes, in particular cyclopentadienyl ruthenium (II) derivatives, catalyze a vast number of transformations in the field of homogenous catalysis. Herein we describe the first synthesis of efficient chiral cationic cyclopentadienyl ruthenium (II) catalysts and their application in enantioselective cycloisomerizations yielding 4H-pyrans. A tremendous counterion effect on the selectivity was observed and subsequently explored, giving rise to a complementary set of neutral cyclopentadienyl ruthenium (II) complexes able to catalyze asymmetric cyclobutene formations.