Mesoporous Ethane-Silicas Functionalized with a Bulky N-Heterocyclic Carbene for Suzuki-Miyaura Coupling of Aryl Chlorides and Benzyl Chlorides

By co-condensation of IMes [IMes = N,N'-bis(2,6-dimethylphenyl)imidazol-2-ylidene]-bridged organosilane and bis(triethoxysilyl)ethane in the presence of template, a new mesoporous ethane silica with a built-in bulky N-heterocyclic carbene (NHC) precursor in the framework was synthesized. N-2 sorption, XRD, and TEM characterizations revealed that the synthesized material had an ordered mesostructure. FT-IR and solid state NMR investigations confirmed that the IMes moiety was covalently integrated with the solid materials. Such a functionalized material was able to coordinate Pd(OAc)(2), leading to an active solid catalyst for Suzuki-Miyaura couplings of challenging aryl chlorides and benzyl chlorides under the relatively mild conditions. By using isopropyl alcohol as solvent and KO'Bu as base, a 78% yield for biphenyl was achieved in the presence of 0.5 mol % Pd at 80 degrees C within 24 h. This solid catalyst could be reused eight times without a significant decrease in activity. The high recyclability may be attributed to the functionalized, stable nanopores that efficiently prevent the in situ formed Pd nanoparticles from the aggregation into the less active large particles in the catalytic reaction. This study not only supplies a novel functionalized periodic mesoporous organosilica (PMO) but also provides an efficient solid catalyst for Suzuki-Miyaura couplings of challenging substrates.