A series of naphthalene-bridged phosphine–sulfonate ligands and the corresponding Pd­(II) complexes [κ2(P,O)-2-(R2P)-1-naphthalenesulfonato]­Pd­(Me)­(dmso) (1, R = Ph; 2, R = o-MeO-C6H4; 3, R = Cy) and Ni­(II) complexes [κ2(P,O)-2-(R2P)-1-naphthalenesulfonato]­Ni­(η3-C3H5) (Ni-1, R = o-MeO-C6H4; Ni-2, R = Cy) have been prepared and characterized. The analogous benzo-bridged phosphine–sulfonate Pd­(II) complex [κ2(P,O)-(R2P)-benzenesulfonato]­Pd­(Me)­(dmso) (2′, R = o-MeO-C6H4) and Ni­(II) complex [κ2(P,O)-(R2P)-benzenesulfonato]­Ni­(η3-C3H5) (Ni-1′, R = o-MeO-C6H4) were prepared for comparison. In ethylene polymerization, complex 2 showed activity of up to 7.5 × 106 g mol–1 h–1, which is among the most active palladium catalysts for ethylene homopolymerization. Under the same conditions, complex 2 showed up to 1 order of magnitude higher catalytic activity than complex 2′, generating polyethylene with slightly smaller molecular weight and similar branching density. The Ni­(II) complex Ni-1 was also more active than complex Ni-1′, generating polyethylene with up to 1 order of magnitude higher molecular weight. In ethylene–methyl acrylate copolymerization, complex 2 showed lower activity, affording a copolymer with higher methyl acrylate incorporation and higher copolymer molecular weight in comparison to complex 2′.

Phosphine-sulfonate based palladium and nickel catalysts have been extensively studied in ethylene polymerization and copolymerization reactions. Previously, the majority of the research works focused on the modifications of the substituents on the phosphorous atom. In this contribution, we systematically demonstrated that the change of the ligand backbone from benzene to naphthalene could greatly improve the properties of this class of catalysts. In the palladium system, this change could increase catalyst stability and polyethylene molecular weights. In the nickel system, this change could dramatically increase the polyethylene molecular weights. Most interestingly, the change in the connectivity of phosphine and sulfonate moieties to the naphthalene backbone could also significantly influence the catalyst properties.