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

Abstract

Cationic [(tmeda)Pd(OEt₂)(Me)][B(Ar_F)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 γ-agostic interactions stabilize the propagating species and permit stepwise monomer insertions to be observed by ¹H NMR spectroscopy. This and earlier studies provide a new proposal for the propagating species in ligand-less late transition metal-catalyzed norbornene polymerizations.