Synthesis of Novel Polyazacryptands for Recognition of Tetrahedral Oxoanions and Their X-ray Structures

Abstract

The Mannich reaction of tris(pyrrolyl-α-methyl)amine (H3tpa) with a mixture of formaldehyde and primary amine hydrochloride (methyl or ethyl) gave two novel macrobicyclic molecules: a hexapyrrolic pentaazacryptand and an unusual pentapyrrolic tetraazacryptand, which were separated by column chromatography and their structures were determined by X-ray diffraction method. The analogous reaction using benzylamine hydrochloride yielded the encapsulated chloride anion complex in 16% yield even after neutralization with aqueous K2CO3, which was also characterized by X-ray diffraction. In addition, the anion binding properties of these macrobicycles were investigated by NMR titration methods, and the binding constants for halides and oxoanions were determined with the EQNMR program. The cavity of the hexapyrrolic pentaazacryptand is flexible and large enough enabling it to form inclusion complexes with the smaller size fluoride ion as well as with the bulkier oxoanions. This was demonstrated by (19)F NMR spectroscopy and by the X-ray structures of the encapsulated sulfate, phosphate, and arsenate ion complexes. Upon complexation the distance between the bridgehead nitrogen atoms changes. Further, anion induced conformational changes were observed in the structures of the oxoanion complexes, particularly in the arsenate structure which represents the first azacryptand encapsulated structure of an arsenate ion. Furthermore, the competition crystallization experiment showed that the phosphate ion complex of the hexapyrrolic pentaazacryptand is the sole crystallization product from an aqueous-organic medium, as confirmed by IR and powder X-ray diffraction studies.

Advances in Anion Supramolecular Chemistry: From Recognition to Chemical Applications

“…[42] Recently, Mani and co-workers described the ability of polypyrrolic cryptands to also bind fluoride in [D 6 ]DMSO ( Figure 6 b). [43] A notable achievement in this field has been the selective recognition of the radioactive pollutant 99 TcO 4 À by a protonated cryptand in acidic water (Figure 6 c). [44] Amendola and co-workers demonstrated by isothermal titration calorimetry that the pertechnetate anion was bound more strongly than either nitrate or chloride by two orders of magnitude.…”

The crystal structure of (4E,11E,31E,38E)-1,4,12,15,18,26,31,39-Octaaza-7,21,24-trihydroxy-penta-cyclo[13·13·13·16,10·120,24·133,37]tetratetraconta-4,6(44),7,9,11,18,20(43),21,23,25,31,33(42),34,36,38-pentadecaene, C36H42N8O3

“…These compounds can act as receptors for anions [3,4], cations [5] or neutral molecules [6]. A Schi -base cryptand was synthesized and its crystal structure was determined.…”

Self assembled macrobicycle and tricycle cages containing pyrrole rings by dynamic covalent chemistry method

“…In recent years, we reported a few cage molecules containing pyrrole rings with carbon or nitrogen as a bridgehead atom by two methods: the Mannich reaction [49][50][51] and DCC, and their anion binding studies (Chart 1) [52]. As a continuation of our interests in synthesizing pyrrole-based molecules, herein we report the synthesis, structural characterization of the macrobicycle and macrotricycle by the DCC method using a trialdehyde molecule.…”