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 10(7) g(polymer) mol(Pd)(-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 (M-n) between 8 x 10(3) and 3 x 10(5) 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 (H-1, C-13, F-19 and P-31) 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.