Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions

Abstract

Supramolecular nanoreactors featuring multiple catalytically active sites are of great importance, especially for asymmetric catalysis, and are yet challenging to construct. Here we report the design and assembly of five chiral single- and mixed-linker tetrahedral coordination cages using six dicarboxylate ligands derived-from enantiopure Mn(salen), Cr(salen) and/or Fe(salen) as linear linkers and four CpZr clusters as three-connected vertices. The formation of these cages was confirmed by a variety of techniques including single-crystal and powder X-ray diffraction, inductively coupled plasma optical emission spectrometer, quadrupole-time-of-flight mass spectrometry and energy dispersive X-ray spectrometry. The cages feature a nanoscale hydrophobic cavity decorated with the same or different catalytically active sites, and the mixed-linker cage bearing Mn(salen) and Cr(salen) species is shown to be an efficient supramolecular catalyst for sequential asymmetric alkene epoxidation/epoxide ring-opening reactions with up to 99.9% ee. The cage catalyst demonstrates improved activity and enantioselectivity over the free catalysts owing to stabilization of catalytically active metallosalen units and concentration of reactants within the cavity. Manipulation of catalytic organic linkers in cages can control the activities and selectivities, which may provide new opportunities for the design and assembly of novel functional supramolecular architectures.

Positive Allosteric Control of Guests Encapsulation by Metal Binding to Covalent Porphyrin Cages

“…Many more complex multidomain regulatory proteins and biological machines that integrate multiple signaling events and long‐range coupled conformational modifications through homotropic or heterotropic binding events have shown to proceed also through allosteric mechanisms . Although the design of 3D hollow structures has led to selective receptors for guest encapsulation and promising molecular nanoreactors, their development as biomimetic allosteric receptors able to control guest complexation through large conformational changes remains a significant challenge . Such a control implies to integrate in the framework of the structure several components with defined regulation and guest binding functions.…”

Asymmetric Catalysis within the Chiral Confined Space of Metal–Organic Architectures

“…Incorporating two or more different catalytic active sites into a single MOC to achieve tandem or sequential catalytic reactions is extremely valuable. Following the above work, Cui and co‐workers designed multifunctional MOCs with multiple available catalytic sites by spatially segregating them inside the confined cavities, and these architectures can then be used for tandem asymmetric catalysis. The single‐ or mixed‐linker tetrahedral cage ( C6 ) with a nanoscale hydrophobic cavity was assembled from enantiopure M(salen) (M = Mn, Cr, and Fe) dicarboxylate ligands and C 3 ‐symmetric Cp 3 Zr 3 clusters ( Figure a–c).…”

“…d) Sequential asymmetric alkene epoxidation/epoxide ring‐opening reactions catalyzed by cage C6 − Mn&Cr. Reproduced with permission . Copyright 2018, American Chemical Society.…”

Recent Advances of MOFs and MOF‐Derived Materials in Thermally Driven Organic Transformations

“…also reported a series of interesting studies focused on chiral catalysis using MOFs . As a continuation of this work, in 2018, they constructed a series of five isostructural MOFs that contained either pure or mixed dicarboxylate struts (Figure ) . The materials consisted of three‐connected Cp 3 Zr 3 SBUs (Cp= n 5 ‐C 5 H 5 ) that were interlinked by individual or combinations of enantiopure Mn(salen), Cr(salen), and/or Fe(salen) struts.…”

“…(B) Schematic representations of cages 1 Mn , 1 Cr and 1 MnCr . (C) Mixed linker cage bearing Mn(salen) and Cr(salen) species for sequential asymmetric alkene epoxidation/epoxide ring‐opening reactions (Mn: light blue; Zr: green; Cr: bright green; N: blue; O: red; C: gray) . Copyright 2018 American Chemical Society.…”