gamma-Agostic interactions stabilize the propagating species in the vinyl addition polymerization of norbornene

Cationic [(tmeda)Pd(OEt2)(Me)][B(ArF)(4)] was synthesized by protonation of (tmeda)PdMe2 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 H-1 NMR spectroscopy. This and earlier studies provide a new proposal for the propagating species in ligand-less late transition metal-catalyzed norbornene polymerizations.