Addition Polymerization of Norbornene-Type Monomers Using Neutral Nickel Complexes Containing Fluorinated Aryl Ligands

The strong Lewis acid B(C 6 F 5 ) 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 C 6 F 5 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(C 6 F 5 ) 2 (PPh 2 CH 2 C(O)Ph), (η 6 -toluene)Ni(C 6 F 5 ) 2, and Ni(2,4,6-tris(trifluoromethyl)phenyl) 2 (1,2-dimethoxyethane). In the case of (η 6 -toluene)Ni(C 6 F 5 ) 2, isolation and characterization of low molecular weight norbornene polymers, using ethylene, indicated that each polymer chain contained a C 6 F 5 headgroup. This points to the initiation step as being the insertion of norbornene into the Ni−C 6 F 5 bond. The polymer microstructure as revealed by 1 H and 13 C NMR spectrometry is entirely different from that produced using the cationic nickel catalyst, [(η 3 -crotyl)Ni(1,4-COD)]PF 6 . This difference in microstructure led to improved mechanical properties for 80:20 copolymers of norbornene and 5-triethoxysilylnorbornene.