Stereoselective Assembly of Gigantic Chiral Molybdenum Blue Wheels Using Lanthanide Ions and Amino Acids

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.

手性多氧金属酸盐（POMs）的合成是一项挑战，原因在于诱导其形成本质上的手性金属-氧框架的难度较大。本研究报告了一系列巨型手性钼蓝（MB）POM簇1-5的立体选择性合成，这些簇通过利用配位镧系离子作为对称破坏者以产生装饰有氨基酸配体的MBs，从而促进了手性框架的形成；这些配体促进了手性MBs的选择性生成。所有化合物均共享相同的框架原型，基于{Mo124Ce4}，该原型形成本质上的手性Δ或Λ构型，由功能化的手性氨基酸的构型所控制。通过圆二色光谱、1H NMR和电喷雾离子迁移-质谱法研究证实了1-5在溶液中的手性和稳定性。此外，{Mo124Ce4} MB的框架不仅作为一种能够捕获传统合成方法无法获得的非手性{Mo8}簇的宿主，还能促进色氨酸原位转化为犬尿氨酸。这项工作展示了我们合成策略在制备具有宿主-客体化学和选择性合成转化能力的大型手性POM簇中的潜力和应用价值。