Compounds of general formula I or Ia ##STR1## or mixtures thereof, wherein the groups P-L-P are a ligand from the group comprising diphosphine and diphosphinite, in which the secondary phosphine groups or phosphinite groups P are coupled via 2 to 4 C atoms, and which form a 5-, 6- or 7-membered ring with the Ir atoms, X, X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.5 and X.sup.6 independently of the others are Cl, Br or I, or X.sup.1 and X.sup.6 and H and X.sup.2, X.sup.3, X.sup.4 and X.sup.5 independently of the others are Cl, Br or I, or X.sup.1 and X.sup.5 and H and X.sup.2, X.sup.3, X.sup.4 and X.sup.6 independently of the others are Cl, Br or I, and M.sup..sym. is an alkali metal cation or quaternary ammonium. The compounds are suitable as homogeneous catalysts for the (preferably) asymmetric hydrogenation of N-substituted imines to secondary amines.