The catalytic CO/styrene and ethylene/methyl acrylate copolymerizations are compared for the first time by applying the same precatalysts. With this aim, PdII neutral, [Pd(CH3)Cl(N--N)], and monocationic, [Pd(CH3)(L)(N--N)][PF6] (L=CH3CN, DMSO), complexes with 1-naphthyl- and 2-naphthyl-substitued α-diimines with both an acenaphthene and a diazabutadiene skeleton as chelating nitrogen-donor ligands (N--N) have been studied. In the case of the complexes with the 1-naphthyl-substituted ligands, syn and anti isomers are found both in solid state and in solution. All the monocationic complexes generate active catalysts for the CO/styrene copolymerization leading to atactic or isotactic/atactic stereoblock copolymers depending on the ligand bonded to palladium. Instead, in the case of the ethylene/methyl acrylate copolymerization only the complexes with the 1-naphthyl-substituted ligands generate catalysts for this reaction.