Search

Au nanoparticles (AuNPs) were immobilized on S-containing amino acids (cysteine and methionine) Mg/Al hydrotalcite clay in both bulk and exfoliated (colloidal) forms. The Au nanoparticles were prepared by a biomimetic method using an anti-oxidant tea extract to reduce the Au salt solution. The performance of bulk and exfoliated clays with Au nanoparticles in aerobic olefin epoxidation was assessed with very interesting results. Both catalysts were very active towards the epoxide products; selectivity was found to be dependent on the catalyst form. The exfoliated catalysts yielded higher product stereoselectivity in the case of limonene epoxidation. These results can be explained by the existence of a confined environment around the AuNPs structures provided by the clay nanosheets wrapping the nanoparticles, modulating how substrates interact with the catalytic active centres. Based on experimental data mechanistic proposals were also rationalized for these catalysts showing how they assist the catalytic process.

Helical mesoporous materials of the MCM-41 type are important materials that can be prepared by onepot synthesis procedures with a co-surfactant. A control of the characteristics at a local level is of the most important in the view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared both helical and regular channel materials from Si-based MCM-41 type. Afterward, a bpy derivative was used as ligand to coordinate MoII/VI. The complexes and the new materials were tested as the catalytic precursors in the epoxidation of cis-cyclooctene, styrene, 1-octene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-butylhydroperoxide (TBHP) as oxidant. Although almost all the catalysts were 100% selective toward the epoxide, the conversions were in general good. The major achievement of these catalysts is an outstanding stereocontrol of the reaction products. In addition, these catalysts were found to be very effective under several circumstances. This is certainly an important contribution for such concept and may render such materials further applications where chiral recognition is important.

[MoX 2 (CO) 3 (pyca)] (X = I, Br) complexes bearing the ligand C 5 H 4 NCH N(CH 2 ) 2 CH 3 (pyca, 2 ) were prepared and characterized by elemental analysis as well as FTIR and 1 H and 13 C solution NMR spectroscopy. Using the modified ligand C 5 H 4 NCH N(CH 2 ) 3 Si(OEt) 3 (pycaSi, 3 ), they were immobilized in MCM-41 ( MCM ) and in mesoporous materials (i.e., periodic mesoporous organosilica [PMO]) and then characterized by powder X-ray diffraction, N 2 adsorption analysis, FTIR, and 29 Si MAS and CP MAS and 13 C CP MAS solid-state NMR spectroscopy. These new materials and complexes were tested in the oxidation of cyclohexene, cyclooctene, and styrene and in the polymerization of styrene and norbornene. All were good catalyst precursors for olefin epoxidation with TBHP ( t -butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs and achieving high conversions in the second run. This finding, combined with the fact that the materials outperformed the homogeneous complexes, make these catalysts very attractive. They combine the selectivity and activity of the homogeneous species with the features of materials. The iodine-containing materials performed better for styrene (100% conversion), and the bromine-containing materials displayed higher conversion for cyclooctene.