Pyridylbenzamidines: versatile ligands for palladium(II)

Recently, we have demonstrated that in copolymerization reactions palladium complexes with nonsymmetric-diimines generate more productive catalysts than those having the corresponding symmetric counterparts, highlighting the positive effect of an unbalance in the steric and electronic properties of the N-donor atoms.1 With the aim to verify the more general validity of this principle, we have now studied bidentate N-donor ligands belonging to the family of pyridylbenzamidines (Figure). While the two molecules with R1 = H were reported in literature,2 the N-methyl substituted derivative is new. The NMR characterization of the molecules pointed out the presence of dynamic phenomena in solution, due to the interconversion of several isomers, including tautomers. The coordination chemistry to Pd(II) was studied on [Pd(cod)(CH3)Cl] and [Pd(cod)(CH3)(CH3CN)][PF6]: depending on the precursor and on the ligand, different coordination compounds were obtained, indicating that these molecules can act both as mono- and bidentate ligands. None of the isolated complexes generated active catalysts either for ethylene homopolymerization or for ethylene/methyl acrylate copolymerization. The deactivation pathway was unraveled.