Abstract
The synthesis of chiral polyoxometalates (POMs) is a challenge because of the difficulty to induce the formation of intrinsically chiral metal-oxo frameworks. Herein we report the stereoselective synthesis of a series of gigantic chiral Mo Blue (MB) POM clusters 1–5 that are formed by exploiting the synergy between coordinating lanthanides ions as symmetry breakers to produce MBs with chiral frameworks decorated with amino acids ligands; these promote the selective formation of enantiopure MBs. All the compounds share the same framework archetype, based on {Mo124Ce4}, which forms an intrinsically chiral Δ or Λ configurations, controlled by the configurations of functionalized chiral amino acids. The chirality and stability of 1–5 in solution are confirmed by circular dichroism, 1H NMR, and electrospray ion mobility–mass spectrometry studies. In addition, the framework of the {Mo124Ce4} MB not only behaves as a host able to trap a chiral {Mo8} cluster that is not accessible by traditional synthesis but also promotes the transformation of tryptophan to kynurenine in situ. This work demonstrates the potential and applicability of our synthetic strategy to produce gigantic chiral POM clusters capable of host–guest chemistry and selective synthetic transformations.
Highlights
Polyoxometalates (POMs) are a unique class of discrete metal oxides with a diversity of structures and properties.[1,2] As such, POMs have a wide range of potential applications from medicine to catalysis and materials science.[3]
During the past two decades, a variety of chiral POM clusters have been designed and synthesized via either chiral resolution and spontaneous resolution of the intrinsically chiral POMs or stereoselective synthesis driven by chirality transfer from chiral organic ligands or metal−organic species.[5]
The chiral functionalization of wheel- or cage-shaped gigantic POMs is interesting, because they could provide confined chiral environments for asymmetric processes such as asymmetric catalysis and chiral recognition and because they could be potentially used as model compounds as “artificial proteins” to mimic functional biological systems.[6]
Summary
Polyoxometalates (POMs) are a unique class of discrete metal oxides with a diversity of structures and properties.[1,2] As such, POMs have a wide range of potential applications from medicine to catalysis and materials science.[3] One focus of POM chemistry is the controlled fabrication of chiral POM clusters that are potential candidates in asymmetric catalysis, chiral separations, sensors and biomedicine.[4] During the past two decades, a variety of chiral POM clusters have been designed and synthesized via either chiral resolution and spontaneous resolution of the intrinsically chiral POMs or stereoselective synthesis driven by chirality transfer from chiral organic ligands or metal−organic species.[5] Despite the synthesis of chiral gigantic POMs, the assembly of systems with chiral frameworks has proved challenging. To the best of our knowledge, there have been no reports of chiral POMs with nuclearity of >100
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