Homogeneous catalysis represents a powerful tool for the controlled synthesis of polymeric materials.1 During the last decades considerable attention has been focused on two polymerization reactions: the CO/alkene copolymerization to yield perfectly alternating polyketones,2 and the ethylene/polar vinyl monomer copolymerization to yield functionalized polyolefins.3 Both reactions are catalyzed by Pd(II) complexes with -diimines as ancillary ligands. Despite the extensive studies in this field, there is a lack of a direct comparison between the two reactions, thus limiting to highlight their analogies and differences.
For several years we have been investigating the CO/vinyl arene copolymerization, and, more recently, we have started to study the ethylene/methyl acrylate (MA) copolymerization, too. With the aim to fill in this gap of knowledge, we have now investigated two series of -diimines (N-N) featured by the acenaphthene (BIAN) or the 1,4-diazabutadiene skeleton (DAB) and sharing the substituents on the N-donor atoms that are 1-naphthyl (1-napht)4 and 2-naphthyl (2-napht) groups (Figure).
These ligands were used to synthesize the corresponding neutral and monocationic Pd(II) complexes [Pd(CH3)(CH3CN)(N-N)][PF6], the latter being tested as precatalysts in both copolymerization reactions. The detailed catalytic study proves that: i. in the CO/vinyl arene copolymerization BIAN ligands generate more productive and more stable catalysts than the DAB derivatives; ii. in ethylene/MA copolymerization DAB-containing catalysts are more productive than BIAN-analogues; iii. for both reactions, regardless to the ligand skeleton, catalysts with 2-naphthyl-substituted ligands show a catalytic behaviour analogous to that of catalysts with meta-substituted aryl-BIANs, while catalysts with 1-naphthyl-substituted ligands show a catalytic behaviour analogous to that of catalysts with ortho-substituted aryl-BIANs.
