BINOL-Containing Chiral Porous Polymers as Platforms for Enantiorecognition

The enantioselective discrimination of racemic compounds can be achieved through the design and preparation of a new family of chiral conjugated BINOL-porous polymers (CBPPs) from enantiopure (R)- or (S)-BINOL derivatives and 1,3,5-tris(4-phenylboronic acid)benzene or 1,3,5-tris(4-ethynylphenyl)benzene, 1,3,5-triethynyl-2,4,6-trifluorobenzene, and tetra(4-ethynylphenyl)methane as comonomers following Suzuki-Miyaura and Sonogashira-Hagihara carbon-carbon coupling approaches. The obtained CBPPs show high thermal stability, a good specific surface area, and a robust framework and can be applied successfully in the fluorescence recognition of enantiomers of terpenes (limonene and a-pinene) and 1-phenylethylamine. Fluorescence titration of CBPPs-OH in acetonitrile shows that all Sonogashira hosts exhibit a preference for the (R)-enantiomer over the (S)-enantiomer of 1-phenylethylamine, the selectivity being much higher than that of the corresponding BINOL-based soluble system used as a reference. However, the Suzuki host reveals a preference toward (S)-phenylethylamine. Regarding the sensing of terpenes, only Sonogashira hosts show enantiodifferentiation with an almost total preference for the (S)-enantiomer of limonene and alpha-pinene. Based on the computational simulations and the experimental data, with 1-phenylethyl-amine as the analyte, chiral recognition is due to the distinctive binding affinities resulting from N center dot center dot center dot H-O hydrogen bonds and the pi-pi interaction between the host and the guest. However, for limonene, the geometry of the adsorption complex is mostly governed by the interaction between the hydroxyl group of the BINOL unit and the C=C bond of the iso-propenyl fragment. The synthetic strategy used to prepare CBPPs opens many possibilities to place chiral centers such as BINOL in porous polymers for different chiral applications such as enantiomer recognition.

Automated summary

This study focuses on the enantioselective discrimination of racemic compounds using a new family of chiral conjugated BINOL-porous polymers (CBPPs). The CBPPs exhibit high thermal stability, a good specific surface area, and a robust framework, making them suitable for fluorescence recognition of enantiomers of terpenes and 1-phenylethylamine. The results show that the CBPPs prepared using the Sonogashira-Hagihara carbon-carbon coupling approach exhibit stronger selectivity towards one enantiomer compared to the reference BINOL-based soluble system.