Luminescent behaviors of bipyridine proline-grafted hybrid bimodal mesoporous silica and its catalytic performance in asymmetric aldol reaction

Synthesis of Extended Bipyridine‐proline Chiral Catalysts and Resulting Effects on the Asymmetric Aldol Reactions of Bulkier Aldehyde Derivatives with Cyclohexanone

“…Noticeably, a lot of reports indicated that the installation of an axially unfixed bipyridine in the designed organocatalysts may afford them favorable conformational properties responsible for efficient chiral induction, and therefore the effect of the steric hindrance originating from reactant or catalyst itself could be minimized . Meanwhile, our preliminary work further testified that the ligands of 2,2′‐bipyridine are easy to be modified and readily combined with functional groups compared with other ligands in current reported, similarly, such as L ‐proline and L ‐phenylalanine as chiral amino acids. In 2013, Zhao et al .…”

“…For these reasons, a large number of chiral catalysts have been recently developed in asymmetric catalytic reactions and chiral recognition . As compared to that of chiral phosphine and amine catalysts, chiral bipyridine catalysts have attracted great attention owing to their highly efficient stereocontrol and unique coordination capabilities . Noticeably, a lot of reports indicated that the installation of an axially unfixed bipyridine in the designed organocatalysts may afford them favorable conformational properties responsible for efficient chiral induction, and therefore the effect of the steric hindrance originating from reactant or catalyst itself could be minimized .…”

Stability of Immobilization of Bipyridine‐proline on Zn‐Modified Bimodal Mesoporous Silicas and Recyclable Catalytic Performance in Asymmetric Aldol Reaction

“…Although pure ZZnBMMs (Figure A‐a) possessed the similar peaks in the range of 250–400 nm, the occurrences of characteristic peaks red‐shifted from 255 to 267 nm, and 311 to 328 nm. These phenomena indicated that Z was successfully immobilized on the mesoporous surface of ZnBMMs . Meanwhile, Figs.…”

“…Other bands at 2926 cm −1 and 1650 cm −1 were ascribed to the C−H and C=O stretching vibrations, respectively. Besides that, as for Z (Figure g), the absorption bands at 1670 cm −1 , 1492 cm −1 were corresponded to C=O stretching vibrations in the –CONH– group and C=N stretching vibrations of pyridine rings, respectively . Compared with that of Z (Figure g), the absorption bands of ZZnBMMs (Figure b) belonging to C=O and C=N stretching vibrations shifted to low wavenumbers by 10 cm −1 and 67 cm −1 , respectively.…”

“…(2 S,2’S)‐N,N’‐([2,2’‐bipyridine]‐3,3’‐diyl) bis(pyrrolidine‐2‐carboxamide) (abbreviated as Z) was synthesized by our collaborator, which presents a good catalytic activity for asymmetric aldol reaction under homogeneous system ,. In our previous studies, a novel heterogeneous chiral catalyst (Z‐BMMs) was prepared via immobilization of Z onto the mesoporous channels of BMMs (Z‐BMMs) by hydrogen bond method, and showed a higher catalytic activity for asymmetric aldol reaction between cyclohexanone and 4‐nitrobenzaldehyde, as compared to that of homogenous catalysts . However, the recycled catalyst sharply deactivated after reusing for only 2 times, leaching of active species in the reactive duration is one of main reasons due to the weak interaction in between Z and surface‐OH of BMMs; Another reason may be related to the characteristic of the unstable mesopores, easily resulting in structure collapse and impurity adsorption.…”