Role of B(C6F5)3 in activating the nickel-methyl complex (η5-C5H5)Ni(CH3)(PPh3) to initiate the vinyl polymerization of norbornene

The Ni-methyl complex (η5-C5H5)Ni(CH3)(PPh3) (1) reacted with B(C6F5)3 to give an unstable contact ion-pair complex with a μ-methyl bridge between the Ni and B atoms. Formation of the B-CH3 bond was confirmed by the reaction of this complex with PPh3 to give [(η5-C5H5)Ni(PPh3)2][B(CH3)(C6F5)3] which was structurally characterized. Spontaneous decomposition of the contact ion-pair complex yielded (η5-C5H5)Ni(C6F5)(PPh3) which is very stable and does not show any reactions with norbornene with or without added B(C6F5)3. 19F NMR study showed that the polynorbornene obtained by the catalysis of 1/B(C6F5)3 system has the C6F5 end-group. A series of reactions, which includes CH3/C6F5 exchange between the Ni and B centers with concomitant dissociation of PPh3 to accept coordination of a norbornene monomer, is proposed as the route to active species that can initiate vinyl polymerization of norbornene.

The Lewis acid B(C6F5)3 attacks (η5-C5H5)Ni(CH3)(PPh3) at the Ni-bound methyl group to form a contact ion-pair complex with Ni-(μ-CH3)-B bond. Successive pathways to generate an active species that can initiate the vinyl polymerization of norbornene are presented based on the reactions of the ion-pair complex.Figure optionsDownload as PowerPoint slide