Vinylic Addition Polynorbornene as a Support for N-Heterocyclic Carbene Palladium Complexes: Catalytic Activity in C–C Cross– Coupling Reactions

Abstract

A vinylic addition polynorbornene (VA-PNB) functionalized with imidazolium groups can be used to synthesize a well-defined supported palladium carbene complex. This complex is a suitable precatalyst for Suzuki and Negishi cross coupling reactions, and it can be reused. A close look to how the catalysis work reveals that palladium aggregates form on the polymer surface after the first catalytic reaction. However, they are not easily washed out and serve as a source of a small amount of homogeneous palladium active species (about 0.1‰ mol) that are responsible for the catalysis. The recovered polymer can be reused several times although increased induction and reaction times are observed in consecutive uses from one run to the next. The reaction was followed up by in situ IR spectroscopy using the ν(C-Br) absorption of the electrophile, so there is no need of an additional functional group to apply this technique.