Addition polymerization of norbornene-type monomers using neutral nickel complexes containing fluorinated aryl ligands

The strong Lewis acid B(C6F5)(3) was found to activate complexes of nickel toward the polymerization of norbornene-type monomers. The active species in this reaction is created by the transfer Of C6F5 from boron to nickel. As a result, a class of neutral, single-component nickel complexes was developed containing two electron-withdrawing aryl ligands that polymerize norbornene and norbornenes with functional pendant groups. Active complexes include Ni(C6F5)(2)(PPh2CH2C(O)Ph), (eta(6)-toluene)Ni(C6F5)(2), and Ni(2,4,6-tris(trifluoromethyl)phenyl)(2)(1,2-dimethoxyethane). In the case of (eta(6)-toluene)Ni(C6F5)(2), isolation and characterization of low molecular weight norbornene polymers, using ethylene, indicated that each polymer chain contained a C6F5 headgroup. This points to the initiation step as being the insertion of norbornene into the Ni-C6F5 bond. The polymer microstructure as revealed by H-1 and C-13 NMR spectrometry is entirely different from that produced using the cationic nickel catalyst, [(eta(3)-crotyl)Ni(1,4-COD)]PF6. This difference in microstructure led to improved mechanical properties for 80: 20 copolymers of norbornene and 5-triethoxysilylnorbornene.