Chiral Induction in a Self-Assembled Pd₄ Coordination Cage with Chiral Guests

Area of Science:

• Coordination chemistry
• Supramolecular chemistry
• Asymmetric catalysis

Background:

• Metal-organic cages (MOCs) exhibit dynamic coordination bonds, enabling structural evolution in response to stimuli.
• This adaptability is key for creating chiral assemblies and advancing asymmetric catalysis.
• Achiral building blocks can be used to construct complex chiral structures.

Purpose of the Study:

• To investigate the self-assembly of a chiral octahedral cage from achiral components.
• To demonstrate guest-mediated chirality transfer for enantioselective cage formation.
• To explore the potential of MOCs in asymmetric catalysis.

Main Methods:

• Self-assembly of a square-planar Pd(II) acceptor and a tetrapyridyl donor.
• Characterization of the resulting cage using circular dichroism (CD) spectroscopy and single crystal X-ray diffraction.
• Encapsulation of chiral aromatic guests in aqueous media via π-π stacking and hydrophobic interactions.

Main Results:

• Formation of a racemic mixture of a chiral octahedral cage, Pd4L2, from achiral precursors.
• Confirmation of the racemic mixture through CD spectroscopy and X-ray diffraction.
• Selective formation of a single enantiopure host-guest complex upon chiral guest encapsulation, demonstrating chirality transfer.

Conclusions:

• Achiral building blocks can self-assemble into chiral metal-organic cages.
• Chiral guests can induce enantioselectivity in the cage structure through host-guest interactions.
• This work provides a novel strategy for generating enantiopure coordination complexes from achiral materials.