Visible‐Light Photocatalysis of Asymmetric [2+2] Cycloaddition in Cage‐Confined Nanospace Merging Chirality with Triplet‐State Photosensitization

Abstract

Although the photodimerization of acenaphthylene (ACE) has been known for 100 years, the asymmetric cycloaddition of its 1‐substituted derivatives is unknown. Herein, we report a supramolecular photochirogenic approach in which a homochiral and photoactive Δ/Λ‐[Pd6(RuL3)8]28+ metal–organic cage (Δ/Λ‐MOC‐16) is used as a supramolecular reactor for the enantioselective exited‐state photocatalysis of 1‐Br‐ACE. Owing to preorganization of the substrates by the supramolecular cage, stereochemical control of the triplet state, and nanospace transfer of energy and chirality, the cycloaddition of ACE proceeded with high selectivity for the formation of anti over syn stereoisomers, whereas the regio‐, stereo‐, and enantioselective cycloaddition of unsymmetrical 1‐Br‐ACE showed effective enantiodifferentiation of a pair of anti head‐to‐head stereoisomers. The enzyme‐mimicking photocatalysis was verified by catalytic turnover, rate enhancement, and competing‐guest inhibition experiments.

Design and Applications of Water-Soluble Coordination Cages

“…The same cage also mediates the stereo- and regioselective photodimerization of 1-bromoacenaphthylene 291 in 1:1 H 2 O/DMSO. The anti -head-to-head dimer 292 was produced in 94% yield, with none of the five other possible isomers observed (Figure b) . The product is chiral and a single enantiomer was favored with up to 88% ee in the presence of Δ- 128 or Λ- 128 .…”

Applications of Nanomaterials in Asymmetric Photocatalysis: Recent Progress, Challenges, and Opportunities

“…In their subsequent work, the chiral MOC‐16 was recently utilized as an effective supramolecular reactor to catalyze the previously unattainable [2+2] enantioselective photocycloaddition from asymmetric acenaphthylene (ACE) derivative. [ 88 ] By taking advantage of confinement effect for substrates preorganization, stereochemical control over triplet‐state and nanospace transfer of energy and chirality, the optically pure MOC‐16 catalyzed cycloaddition of asymmetric 1‐Br‐ACE to give highly regio‐, stereo‐, and enantioselective product with both high conversion (99%) and excellent ee value (86%). Overall, these studies have successfully constructed photoactive chiral coordination cages as efficient catalysts and furthermore open a door toward the efficient asymmetric photocatalysis.…”

Photooxidase Mimicking with Adaptive Coordination Molecular Capsules

“…Motivated by the excellent activity of natural enzymes, scientists have constructed enzyme mimics to reproduce their structures − and functions at the molecular level. − Self-assembled supramolecular architectures, particularly molecular capsules, offer a powerful platform to imitate the property of natural enzymes. − The incorporation of different functional units into the artificial assemblies has been proven to be convenient in affording enzyme-like nanoreactors. − While changing the building blocks can give rise to various structures and properties of the supramolecular assemblies, − capsules with closed cavities wrapped by strict rigid ligand structure are unfavorable toward catalysis because of inefficient substrate binding and/or severe product inhibition. Currently, more efforts have been invested in constructing stimuli-responsive supramolecular hosts with adaptive confined cavities. − However, only a few examples are known for chemical transformations, particularly catalytic transformations, by such allosteric hosts. − On the other hand, considerable advances have been made in supramolecular photocatalysis, − …”