Gamma-agostic interactions stabilize the propagating species in the vinyl addition polymerization of norbornene.

Cationic [(tmeda)Pd(OEt(2))(Me)][B(Ar(F))(4)] was synthesized by protonation of (tmeda)PdMe(2) and allowed for the first time the nature of the propagating species in the vinyl addition polymerization of norbornene to be discerned. In this system gamma-agostic interactions stabilize the propagating species and permit stepwise monomer insertions to be observed by (1)H NMR spectroscopy. This and earlier studies provide a new proposal for the propagating species in ligand-less late transition metal-catalyzed norbornene polymerizations.