BINOL-Containing Chiral Porous Polymers as Platforms for Enantiorecognition

Abstract

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, 1,3,5triethynyl-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 α-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 α-pinene. Based on the computational simulations and the experimental data, with 1-phenylethylamine as the analyte, chiral recognition is due to the distinctive binding affinities resulting from N•••H−O hydrogen bonds and the π−π 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 isopropenyl 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.

Regioselective Substitution of BINOL

“…When ( S )-6,6′- t Bu 2 BINOL diethyl ether was treated with bromine in CH 2 Cl 2 solution at −78 °C, ( S )- 99 with 4.4′-dibromination was obtained in 99% yield . The cross-coupling reaction of ( S )- 99 and its adamantanyl analogue ( R )- 100a with aryl tris-boronic acids and aryl tris- or tetra-terminal alkynes were used to make chiral porous polymers such as ( R )- 100b for enantioselective fluorescent recognition of limonene, α-pinene, and a chiral amine.This paper reports that the bromination of 6,6′- t Bu 2 BINOL diethyl ether occurs at the 4,4′-position, which is in contrast to the reported 3,3′-dibromination of 6,6′- t Bu 2 BINOL to form ( S )- 122 , where a single crystal X-ray analysis has confirmed the structure (see Scheme ).…”

Chiral Porous Organic Frameworks: Synthesis, Chiroptical Properties, and Asymmetric Organocatalytic Applications

“…BINAPcontaining POFs were prepared using copper-catalyzed alkyne−azide click reaction starting from diethynyl 2,2′-bis(diphenylphosphino)-1,1′-binaphthlyl (BINAP) compound (Scheme 3D) [51]. POFs composed of BINOL building blocks have been prepared using various couplings [52], such as FeCl3-induced oxidative homocoupling polymerization (Scheme 3E) [53] or Suzuki coupling (Scheme 3E) [54]. Proline-functionalized building The most straightforward approach is (i) using chiral building blocks as the starting materials, as this approach ensures the full incorporation of the chiral moieties into the material [33][34][35][36][37][38].…”

Construction of a pillar[5]arene-based supramolecular chiral polymer linked to aminophosphine salt for chiral recognition of enantiomers of mandelic acid

“… 9 Currently, many studies have shown that, the host molecule selectively binds to the enantiomer of the guest molecule through non-covalent interactions such as hydrogen bonding, 10 metal coordination, π–π packing, 11 and/or electrostatic interactions. 12 So a number of chiral systems are reported for enantioselective recognition and separation, such as chiral metal–ligand complexes, 13 chiral polymers, 14 micelles, 15 and vesicles. 16 Supramolecular chiral polymers, as a good host material, provide more possibilities for chiral recognition.…”