Multi-Layered, Covalently Supported Ionic Liquid Phase (mlc-SILP) as Highly Cross-Linked Support for Recyclable Palladium Catalysts for the Suzuki Reaction In Aqueous Medium

摘要

The reaction between an excess of 1,4-bis(3-vinylimidazolium-1-yl) bromide and a mercap-topropyl-modified amorphous silica gel or ordered mesoporous silica SBA-15 in the presence of azobis-isobutyronitrile (AIBN) afforded new materials, which have a high loading of imidazolium moieties. These materials, which contain a highly cross-linked polymeric network, have been denoted as multi-layered, covalently supported ionic liquid phase (mlc-SILP) and have been used as support for palladium catalysts containing a high loading of the metal (10 wt%). Such materials were characterized by several techniques (~(13)C magic angle spinning nuclear magnetic resonance, the Brunauer-Emmett-Teller technique, small-angle X-ray scattering, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy). The presence of a homogeneous distribution of palladium nanoparticles was established. The palladium catalysts displayed good activity allowing the synthesis of several bi-phenyl compounds in high yields working with only 0.1 mol% of palladium loading at mild temperatures (room temperature or 50 °C) in ethanol/water. Reactions carried out on a 10-mmol scale required only 10 mg of catalysts. Good recyclability was observed.