Palladium(II) salts containing [PdCl4]2– and [Pd2Cl6]2– ions as pre-catalysts for the vinyl-polymerization of norbornene—evidence for the in situ formation of PdCl2 as the active species

The polymerization behaviour of a new series of palladium(II) pre-catalysts in the vinyl-polymerization of norbornene has been investigated. Compounds containing [PdCl4]2- or [Pd2Cl6]2- anions and the organic cations [K(18-crown-6)]+, [H3O(18-crown-6)]+, [Ph3PCH2C(O)CH3]+ or [Him]+(im = imidazole) can be activated with the Lewis acids methylalumoxane (MAO), tris(pentafluorophenyl)borane, B(C6F5)3 or a combination of B(C6F5)3/triethylaluminum (TEA). The catalytic systems show very high norbornene polymerization activities of up to 107 gpolymer molPd-1 h-1. In the case of an activation with B(C6F5)3 alone it is possible to obtain soluble palladium-catalyzed poly(norbornene)s which exhibit a fully saturated polymer backbone and a molar mass (Mn) between 8 × 103 and 3 × 105 g mol-1. The activation process of the pre-catalyst [Ph3PCH2C(O) CH3]2[Pd2Cl6](2C) in combination with B(C6F5)3 can be followed by multinuclear (1H, 13C, 19F and 31P) NMR investigations and points to the in situ formation of PdCl2 which then represents the active species for the polymerization process. The X-ray structure of compound 2C is reported.