π-AllylPdCl-Based Initiating Systems for Polymerization of Alkyl Diazoacetates: Initiation and Termination Mechanism Based on Analysis of Polymer Chain End Structures

Polymerization of ethyl and benzyl diazoacetates (EDA and BDA) initiated with π-allylPdCl-based systems [π-allylPdCl/NaBPh4, π-allylPdCl/NaBArF4 (ArF = 3,5-{CF3}2C6H3), and π-allylPdCl] is described. Initiation efficiencies of the π-allylPdCl-based systems are much higher than those of the previously reported (NHC)Pd/borate (NHC = N-heterocyclic carbene) systems, and the new systems are capable of polymerizing the alkyl diazoacetates at low temperatures(0 ∼ −20 °C), where the (NHC)Pd/borate systems cannot initiate the polymerization. MALDI–TOF–MS analyses of the polymers obtained from EDA provide information for the chain-end structures of the polymers, based on which initiation and termination mechanisms are proposed. Interestingly, EDA polymerization by the π-allylPdCl-based systems in the presence of alcohols (EtOH, nPrOH, and nBuOH) or water was found to afford RO- or HO-initiated polymers as major products, as confirmed by MALDI–TOF–MS analyses.