Bidentate P,P- and N,P-ligands derived from inexpensive and commercially available chiral source (R,R)-1,2-diaminocyclohexane, have been tested in the asymmetric Rh-catalyzed addition of diphenylsilane to acetophenone. Studies on the reactivity of these ligands towards the rhodium precursor [Rh(cod)Cl](2) (cod = cycloocta-1,5-diene) have shown that either monomeric, or dinuclear complexes, or both can be found in the solution. The structure of the cationic complex [Rh(cod)(3a)]PF6 (12), has been elucidated by X-ray analysis. The presence in the reaction mixture of different rhodium complexes which act as precatalysts, influences the activity and stereoselectivity of the process. (C) 2004 Elsevier B.V. All rights reserved.