Neutral and bis-cationic palladium(H) complexes with 1,2-bis(di(2-methoxyphenyl)phosphino)ethane (o-MeO-dppe) and 1,3-bis(di(2-methoxyphenyl)phosphino)propane (o-MeO-dppp) have been synthesized and employed to catalyze the CO-ethylene copolymerization reaction in either protic or aprotic solvents. A comparison of the catalytic performance of these complexes with that of analogous precursors stabilized by 1,2-bis(diphenylphosphino)ethane (dppe) and 1,3-bis(diphenylphosphino)propane (dppp) ligands has shown significant differences in terms of catalytic productivity and molecular weight. In situ and operando high-pressure NMR experiments have provided valuable information on catalysis resting states and intermediates and have contributed to rationalize the observed productivity as well. (c) 2006 Elsevier B.V. All rights reserved.