Aerosol-Assisted Rapid Fabrication of a Heterogeneous Organopalladium Catalyst with Hierarchical Bimodal Pores.

Abstract

Heterogeneous organometallic catalysts with well-defined active sites and hierarchical pores hold tremendous promise for efficient and eco-friendly chemical processes. However, the simple and scalable preparation of these materials remains difficult to date, which has hampered a more broad application scope. Herein, we reported a low-cost, rapid, and scalable aerosol-assisted assembly approach for the synthesis of a well-defined PdDPP (PdCl2(PPh2(CH2)2))_ complex-containing benzene-bridged organosilica-based catalyst with a hierarchical bimodal micro-macroporous structure. This novel material was realized by using Pd(II) organometallic silane (Pd[PPh2(CH2)2Si(OEt)3]2Cl2) as the active species, organosilane 1,4-bis(triethoxysilyl)benzene (Ph[Si(OEt)3]2) as the silicate scaffold and the surfactant cetyltrimethylammonium bromide and the inorganic salt NaCl as the dual templates on a home-built aerosol spraying-instrument. Multiple techniques including X-ray photoelectron spectroscopy and solid-state NMR spectra revealed that the organopalladium complex with a well-defined molecular configuration of major trans model and minor cis model existed in the phenyl-functionalized silica material. As expected, it efficiently promoted a variety of important carbon-carbon cross-coupling transformations including Tsuji-Trost, Sonogashira, and Suzuki reactions in pure water without the assistance of any additives. In comparison with the homogeneous catalyst PdCl2(PPh2CH3)2, it even exhibited enhanced activity and selectivity in some cases owing to the unique confinement effect and the shape selectivity generated from the hierarchical porous structure. Meanwhile, it was easily recycled and reused eight times without the loss of its activity.