The preparation and the characterization of palladium(II) neutral dichloro complexes [PdCl2(P boolean AND P')] 1a-d and cationic disolvento complexes [Pd(P boolean AND-P')(H2O)(2)](OTf)(2) 3a-d containing non-symmetrical C-s-symmetrical diphosphines are reported. Terpolymerization of ethene, propene and carbon monoxide was carried out with the catalyst precursors 3a-d. In the test of each catalyst precursor the ethene pressure was systematically increased, while the propene concentration and carbon monoxide pressure were kept constant. The produced terpolymers were characterized by means of H-1 and C-13 NMR spectroscopy. The catalytic activity of the systems tested is discussed. The structure of the produced terpolymers is analyzed via NMR spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.