Inclusion of Amine Isomers with Open-Chain Hosts Having a Partial Structure of p-tert-Butylthiacalixarene

Abstract

Porous materials, which can capture a specific compound from a hard-to-separate molecular mixture, are strongly desired for practical separation and purification processes. Aiming to develop such materials, we have investigated the performance of our original host compounds, [3,3′-thiobis­(5-tert-butyl-2-hydroxybenzene)-1,1′-diyl]­diacetic acid (2) and its monopropyl ester (3), in discriminating among regio- or stereoisomers of three groups of amines, 2-, 3-, and 4-methylpyridine, 2-, 6-, and 8-methylquinoline, and cis- and trans-4-cyclohexanamine. Diacid 2 selectively included 4-methylpyridine in hexane and 3-methylpyridine in toluene in competitive inclusion among the three regioisomers. Mechanistic studies revealed that the inclusions of 3- and 4-methylpyridine are favored under kinetic and thermodynamic control, respectively. Solvent-dependent switching in guest selectivity was also observed in competitive inclusion among the methylquinoline isomers with diacid 2, whereas trans-4-methylcyclohexanamine was selectively included over the cis-isomer by monoester 3, as well as diacid 2, regardless of the solvent employed. X-ray crystallographic analysis of the resulting inclusion crystals suggests that the wide guest scope of the host compounds originates from their flexible ability to form complexes with amines.

Selective Inclusion of Cyclohexanediol Stereoisomer by Crystals of Open-Chain Diol-Type Host Based on a Partial Structure of p-tert-Butylthiacalixarene

“…72−76 Carboxylic acid-type hosts, such as compound 1, can selectively include aromatic amine isomers via the formation of salt complexes with pseudocyclic structures (Chart 1). 73,74 In the crystal, compound 1, in which two phenolic moieties adopt an anti conformation, forms a onedimensional chain through hydrogen bonds among the carboxy groups, and these chains are stacked to form a sheet structure. Therefore, there are no voids that include guest molecules in the guest-free crystal.…”

“…Therefore, we focused on the properties of linear-type host molecules − and studied a selective inclusion method using open-chain-type host molecules with a 2,2′-thiodiphenol moiety, which is a partial structure of p - tert -butylthiacalix­[4]­arene. − Carboxylic acid-type hosts, such as compound 1 , can selectively include aromatic amine isomers via the formation of salt complexes with pseudocyclic structures (Chart ). , In the crystal, compound 1 , in which two phenolic moieties adopt an anti conformation, forms a one-dimensional chain through hydrogen bonds among the carboxy groups, and these chains are stacked to form a sheet structure. Therefore, there are no voids that include guest molecules in the guest-free crystal.…”