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.