Preparation of heterogeneous catalysts supported on mesoporous molecular sieves modified with various N-groups and their use in the Heck reaction

A series of supported catalysts has been prepared from palladium(II) acetate and mesoporous molecular sieves bearing various N-donor groups at their surface and probed in the Heck coupling between n-butyl acrylate and bromobenzene to give n-butyl cinnamate. The results indicate that the catalytic activity as well as the amount of leached metal depends on the nature of the nitrogen modifying group. The best catalysts were obtained from the sieves bearing the ≡SiCH2CH2CH2NH2 or ≡SiCH2CH2CH2NHCH2CH2NEt2 groups at the surface. When combined with sodium acetate, the former catalyst provided the coupling product with conversions as high as 84% under microwave irradiation for 30 min and 84% under solvothermal conditions (160 °C/4 h) whereas application of the latter catalyst resulted in conversions 90% and 71% under identical reaction conditions (all at 1 mol% Pd loading). Conversions of 5% and 14%, respectively, were achieved with these catalysts under microwave conditions without an external base, which corresponds to the consumption of 77% and 88% amine sites by the liberated HBr. The particle growth leading to the catalyst deactivation was studied by high-resolution transmission electron microscopy and by X-ray powder diffraction.

Catalytic performance of supported catalysts obtained from mesoporous molecular sieves modified with N-donor groups and palladium(II) acetate in the Heck coupling is controlled by the modifying group. The most efficient catalyst possessing ≡SiCH2CH2CH2NH2 and ≡SiCH2CH2CH2NHCH2CH2NEt2 groups afforded the coupling product in conversion as high as 90% under microwave irradiation for 30 min and up to 84% under solvothermal conditions (160 °C/4 h) when combined with sodium acetate. The latter catalyst also displayed considerable bifunctional (i.e., metal-containing and basic) character. Figure optionsDownload as PowerPoint slide