A periodic mesoporous organosilica (PMO) with chiral cyclohexyldiamine‐based nickel(II) complexes incorporated within the silica framework was prepared through a co‐condensation of (1R,2R)‐cyclohexyldiamine‐derived silane and Ph‐bridged silane followed by complexation of nickel(II) bromide in the presence of (1R,2R)‐N,N′‐dibenzylcyclohexyldiamine. Structural analyses by X‐ray powder diffraction, nitrogen sorption and transmission electron microscopy disclosed its orderly mesostructure while characterization by solid‐state NMR and X‐ray photoelectron spectroscopy demonstrated the well‐defined single‐site chiral bis(cyclohexyldiamine)‐based nickel(II) active centers incorporated within the PMO material. In particular, as a heterogeneous chiral catalyst, this periodic mesoporous organosilica showed high catalytic activity and excellent enantioselectivity in asymmetric Michael addition of 1,3‐dicarbonyl compounds to nitroalkenes (more than 92% conversions and up to 99% ee values). More importantly, this heterogeneous catalyst could be recovered easily and reused repeatedly nine times without obviously affecting its ee value, showing good potential for industrial applications.
An imidazolium-based bifunctional heterogeneous catalyst exhibits excellent catalytic efficiency in asymmetric transfer hydrogenation of aromatic ketones in aqueous medium. The superior catalytic performance and the enhanced enantioselectivity is attributed to the synergistic effect of salient imidazolium phase-transfer function and the confined nature of the chiral organoiridium catalyst.
Phase‐transfer featured, imidazolium‐based, organic‐inorganic hybrid silica represents a novel functionalized platform with particularly attractive features in asymmetric catalysis. Herein, we report a chiral organorhodium‐functionalized heterogeneous catalyst. As demonstrated in the studies, it displays comparable or higher catalytic activity and enantioselectivity than its homogeneous counterpart in asymmetric transformations. The superior catalytic performance is attributed to the synergistic effect of the salient imidazolium phase‐transfer character and the confined chiral organorhodium catalytic nature in addition to the merits of mesoporous silica. Furthermore, it is more robust than other silica‐derived heterogeneous systems and can be conveniently recovered and reused at least 10 times without loss of its catalytic efficiency. These features render the catalyst particularly attractive in practice of organic synthesis. The outcomes from the study clearly show that the strategy described here offers a general approach to immobilization of chiral ligand‐derived silane onto the phase‐transfer featured imidazolium‐based organic‐inorganic hybrid silica materials with significant improving catalyst efficiency.
A blaze of chirality The cover picture shows a phase-transfer featured imidazolium-based organic-inorganic hybrid silica as an efficient heterogeneous catalyst for promoting the highly enantioselective Michael addition of malonates to nitrostyrenes. In their Full Paper on p. 1784 ff., G. Liu, W. Wang et al. reveal how their hybridized catalyst is exceptionally stable and can be recovered and recycled easily without loss of activity or selectivity.
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