Polymerization of Diazoacetates Initiated by the Pd(N-arylmaleimide)/NaBPh4 System: Maleimide Insertion into a Pd-C Bond Preceding to Initiation Leading to Efficient a-Chain-End Functionalization of Poly(alkoxycarbonylmethylene)s

Three new N-arylmaleimide-based Pd(0) complexes [Pd(N-phenylmaleimide)2(2,5-norbornadiene) (1), Pd(N-2,6-difluorophenylmaleimide)2(2,5-norbornadiene) (2), and Pd(N-2,6-difluorophenylmaleimide)2(dibenzylideneacetone) (3)] were prepared and used as an initiator in conjunction with NaBPh4 [Pd(N-arylmaleimide)/NaBPh4 system] for polymerization of diazoacetates. The Pd(N-arylmaleimide)/NaBPh4 system polymerized a series of diazoacetates (ethyl, benzyl, and cyclohexyl diazoacetates) to yield polymers in moderate to good yield, particularly showing a high activity for cyclohexyl diazoacetate. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis and other experimental observations revealed the incorporation of one N-arylmaleimide molecule coordinated on the Pd center into the alpha-chain end of the polymers obtained with the initiating system, indicating that the initiating species of the polymerization was generated by insertion of N-arylmaleimide into a Pd-Ph linkage, which was first formed by the reaction of the Pd(0) complex with NaBPh4, and that the initiating system would enable syntheses of alpha-chain-end-functionalized poly(alkoxycarbonylmethylene)s.