Gold nanoparticles stabilized by task-specific ionic complexes: Quasi-homogeneous catalysts with self-separating nature for aerobic epoxidation of styrene

• Gold nanoparticles were stabilized by task-specific ionic complexes.
• Dioxygen-mediated styrene epoxidations over the above catalysts were studied.
• The catalysts showed unique thermo-regulated self-separation nature.
• Conversions >30% with the selectivities >70% to the epoxide could be achieved.
• The catalysts could be reused for four times without significant loss of activity.

A series of imidazolium cation-based task-specific ionic complexes (TSICs) containing polyethylene glycol (PEG) chains and organic moieties with affinity to Au species were synthesized to stabilize gold nanoparticles (GNPs). With toluene as reaction media, the resultant GNP/TSIC catalysts showed a unique thermoregulated self-separating nature in the dioxygen-mediated epoxidation of styrene. The effects of PEG chain length and operational variables in the epoxidation on the catalytic performance of GNP/TSIC catalysts were investigated systematically. It was found that extending the PEG chain was conducive not only to the formation of small and well-dispersed GNPs but also to the fabrication of GNP/TSIC catalysts with apparent thermoregulated self-separating nature. Under optimum operational variables, a GNP/TSIC catalyst based on a vinyl-functionalized TSIC containing a PEG6000 chain achieved 32.9% styrene conversion with 72.0% selectivity to the epoxide; meanwhile, relevant turnover frequency was as high as 2.47 mol (Au)g−1 h−1. Moreover, the catalyst could be reused four times without significant loss of activity.

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