The Inhibiting Influence of Aromatic Solvents on the Activity of Asymmetric Hydrogenations We would like to thank the Deutsche Forschungsgemeinschaft as well as the Fonds der Chemischen Industrie for their generous support of this work. We are also indebted to Prof. Dr. U. Rosenthal and Dr. D. Selent for helpful discussions. Franz Hein prepared bis(η6-arene)-chromium(I)-complex cations already in 1919; their true structure as hexahapto complexes was only realized more than 35 years later.