Selective Isolation of Polycyclic Aromatic Hydrocarbons by Self-Assembly of a Tunable N→B Clathrate

Abstract

The combination of one dipyridyl linker [1,2-di(4-pyridyl)ethylene (DPE), 1,2-di(4-pyridyl)ethane (DPEt), or 4,4′-azopyridine (DPA)] with two molecules of arylboronate ester 1 produced dinuclear Lewis-type N→B adducts that can act as acyclic host for polycyclic aromatic hydrocarbons (PAHs) in the solid state. Nine crystalline solids of composition PAH@adduct (i.e., one PAH per adduct) were obtained from solutions containing a single PAH. On the basis of the single-crystal X-ray diffraction analysis of the compound ANT@A1 (ANT = anthracene; A1 = adduct being composed of DPE and two boronate esters 1), the PAH inclusion selectivity is related to a size-fitting adaptation to an octaedral-shaped pocket assembled by CH-π interactions between fragments of the diamine and the arylboronate ester 1. The resulting reversible organic clathrates can perform "catch and release" cycles of PAHs such as pyrene and can sequester selectively PAHs from mixtures in solution.T he molecular recognition of polycyclic aromatic hydrocarbons (PAHs) is a challenging issue given the variety of sizes, shapes, and properties of these widespread materials. 1 PAHs are among the most intensively studied pollutants in the environmental analysis of air, water, food, and solid-waste samples. Methods for quantitative separation and detection of PAHs often rely on traditional chromatographic and solventextraction protocols. 2 A well-established supramolecular approach to bind PAHs in solution consists of the use of polycationic macrocycles and cages derived from extended viologens, which are assembled covalently 3 or through metal coordination. 4 The association constants of these host−guest complexes in water and polar solvents range between 10 1 and 10 6 M −1 , and a significant number of X-ray crystal structures of such complexes has been reported. Yet these elegant supramolecular receptors were made in multistep synthetic procedures 3 or involved costly transition metals. 4 Thus, it is still a demanding task to develop simple methods to selectively detect PAHs, and also to be able to recover them quantitatively as a single (or multiple) PAH from mixtures in solution. 1,2 In the past decade, various research groups have comprehensively explored the interaction of aromatic amines with boronate esters and boroxines to provide a broad variety of discrete and polymeric materials, such as macrocycles, 5 nanostructures, 6 coordination polymers, 7 and gels. 8 Hence, supramolecular assembly based on dative N→B interactions is recognized as a useful strategy for the generation of complex systems, and given its thermodynamic stability (−11 to −38 kJmol −1 ) 6,7 and kinetic lability in polar coordinating solvents, the central N→B binding motif can be compared to a typical noncovalent interaction. The potential of this approach is well exemplified by the prismatic organic cages assembled via N→B bonds that were able to encapsulate triphenylene or coronene in the solid state. 6c These previous reports have also evidenced that simple arylmonoboronate esters ...

Efficiently self-healing boronic ester crystals

“…1A ). 29 The product was recrystallized from n -hexane to yield translucent planks of up to 3 cm in length. The crystals can be bent plastically, twisted elastically, and shaped into arbitrary morphologies, as demonstrated by using crystals to write in English and Arabic ( Fig.…”

Boron–Nitrogen Double Tweezers Comprising Arylboronic Esters and Diamines: Self‐Assembly in Solution and Adaptability as Hosts for Aromatic Guests in the Solid State

“…In order to gain insight into the driving forces concerning the host‐guest interactions in these cocrystals, intermolecular interaction energies were computed using the tools implemented in CrystalExplorer . The interaction energies computed for various pairs of host:guest aggregates in cocrystals ( 7 ) 2 BiPy⊃BEN, ( 4 ) 2 DPE⊃ANT, ( 4 ) 2 DMBiPy⊃TTF, and ( 4 ) 2 DMBiPy⊃PYR are gathered in Table . These complexes are representative of the ensembles in these crystal structures (see Figure and SI).…”

“… Tweezer:guest aggregates extracted from the crystal structures of cocrystals ( 7 ) 2 BiPy⊃BEN, ( 4 ) 2 DPE⊃ANT, ( 4 ) 2 DMBiPy⊃TTF, and ( 4 ) 2 DMBiPy⊃PYR. Interaction energies were computed for each assembly as summarized in Table .…”

“…Interestingly, guest recognition may occur in both cavities within this framework resembling a double‐tweezer host, and structural syn / anti ‐isomerism is feasible, which might enable the encapsulation of even two different guest molecules (Scheme c). Moreover, these double‐tweezer hosts were shown to perform “catch‐release” cycles of polycyclic aromatic hydrocarbons (PAHs) such as pyrene from solution mixtures, to accomplish the separation of o ‐xylene from an equimolar mixture of o ‐, m ‐ and p ‐xylene isomers by enrichment through fractional crystallization, and to behave as molecular scavengers for the selective removal of sulfur‐based aromatics such as thiophene …”

Channel Confinement of Aromatic Petrochemicals via Aryl–Perfluoroaryl Interactions With a B←N Host

“…As part of our efforts to investigate boron-based host materials (Herrera-España et al, 2015; Campillo-Alvarado et al, 2018c), we report the synthesis and channel confinement properties of a highly electron-deficient adduct ( be-pf-sbz ) (Scheme 1A). The boron host be-pf-sbz is primarily sustained by a B←N bond between phenylboronic acid catechol ester ( be ) and trans -pentafluorostilbazole ( pf-sbz ).…”