Multi-layered, covalently supported ionic liquid phase (mlc-SILP) as highly cross-linked support for recyclable palladium catalyst for the Suzuki reaction in aqueous medium

Reaction between an excess of 1,4-bis-(3-vinylimidazolium-1-yl) bromide and a mercaptopropyl-modified amorphous silica gel or ordered mesoporous silica SBA-15 in the presence of azobisisobutyronitrile (AIBN) afforded new materials, which have a high imidazolium moiety loading. 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 (13C Magic Angle Spinning Nuclear Magnetic Resonance, Brunauer-Emmett-Teller technique, small-angle X-ray scattering, X-ray diffraction, X-ray photoelectron spectroscopy, 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 biphenyl compounds in high yields working with only 0.1 mol% of palladium loading at mild temperature (r.t. or 50°C) in ethanol/water. Reactions carried out on 10 mmol scale required only 10 mg of catalysts. Good recyclability was observed.