Catalysts of Suzuki Cross-Coupling Based on Functionalized Hyper-cross-linked Polystyrene: Influence of Precursor Nature
This paper describes synthesis of Pd-containing catalysts of Suzuki cross-coupling based on amino-functionalized hyper-cross-linked polystyrene at variation of Pd precursor nature (PdCl2, PdCl2(CH3CN)(2), or PdCl2(PhCN)(2)). The investigation of the influence of palladium, oxidation state (Pd(II) or Pd(0)) and form (Pd-n dusters or Pd nanoparticles) on the rate of Suzuki cross-coupling of 4-bromoanisole and phenylboronic acid is discussed. Developed catalysts are shown to allow achieving, conversion of 4-bromoanisole higher than 98% under mild reaction conditions. Independently of the precursor nature, Pd(II) is mainly responsible for observed catalytic activity. However, preliminary reduction of catalysts with H-2 results in formation of a large number of Pd-n. clusters, the contribution of which in the Suzuki reaction becomes predominant.