Immobilization of chiral oxazaborolidine catalyst over highly ordered 3D mesoporous silica with Ia3d symmetry for enantioselective reduction of prochiral ketone.

Here we demonstrate for the first time the encapsulation of a chiral oxazaborolidine complex in the 3D mesoporous channels of an amine functionalized KIT-6 material via covalent bonding through a post-synthetic approach. The physico-chemical properties of the pure and immobilized KIT-6 catalysts were obtained by various techniques such as XRD, nitrogen adsorption, HRSEM, UV-Vis diffuse reflectance spectroscopy, and FT-IR spectroscopy. It has been found that the structural stability of the KIT-6 was not affected even after the immobilization of a significant amount of chiral ligand inside the mesoporous channels of the support. However, the values of structural parameters such as the specific surface area and the specific pore volume of the KIT-6 support was significantly lower than the pure KIT-6 support. The chemical interaction between the chiral ligand inside the mesochannels and the KIT-6 support was also confirmed by UV-Vis and FT-IR spectroscopy. The chiral catalytic performance of the immobilized catalysts for the enantioselective reduction of aromatic prochiral ketones was demonstrated and the results were compared with chiral catalyst immobilized supports with uni-dimensional porous structures, such as MCM-41 and SBA-15. Among the catalysts studied, chiral catalyst immobilized KIT-6 showed the highest performance with a high product yield and a high enantioselectivity due to its 3D porous structure with two continuous and interpenetrating systems of chiral channels and an interwoven 3D cylindrical type pores of Ia3d symmetry. The catalyst also exhibited much better recycling capability than other chiral catalyst supported mesoporous materials used in the study.

Iron oxide nanoparticles embedded onto 3D mesochannels of KIT-6 with different pore diameters and their excellent magnetic properties.

Here, we report the results of our detailed study on the fabrication of iron oxide magnetic nanoparticles confined in mesoporous silica KIT-6 with a 3D structure and large, tunable pore diameters. It was confirmed by XRD, nitrogen adsorption, high-resolution (HR) TEM, and magnetic measurements that highly dispersed iron oxide nanoparticles are occupied inside the mesochannels of KIT-6. We also demonstrated that the size of the iron oxide nanoparticle can be controlled by simply changing the pore diameter of the KIT-6 and the weight percentage of the iron oxide nanoparticles. The effect of the weight percentage and size of the iron oxide nanoparticles, and the textural parameters of the support on the magnetic properties of iron oxide/KIT-6 has been demonstrated. The magnetization increases with decreasing iron content in the pore channels of KIT-6, whereas coercivity decreases for the same samples. Among the KIT-6 materials studied, KIT-6 with 7.5 wt % of iron showed the highest saturation magnetic moment and magnetic remanence. However, all the samples register a coercivity of around 2000 Oe, which is generally observed for the hard magnetic materials. In addition, we have found a paramagnetic-to-superparamagnetic transition at low temperature for samples with different iron content at low temperature. The cause for this exciting transition is also discussed in detail. Magnetic properties of the iron oxide loaded KIT-6 were also compared with pure iron oxide and iron oxide loaded over SBA-15. It was found that iron oxide loaded KIT-6 showed the highest magnetization due to its 3D structure and large pore volume. The pore diameter of the iron oxide loaded KIT-6 support also plays a critical role in controlling the magnetization and the blocking temperature, which has a direct relation to the particle diameter and increases from 48 to 63 K with an increase in the pore diameter of the support from 8 to 11.3 nm.