Synthesis, Characterization, and Binding Properties of Novel Penta-Crown Ethers

Abstract

S y n t h e s i s , C h a r a c t e r i z a t i o n , a n d B i n d i n g P r o p e r t i e s o f N o v e l P e n t a -C r o w n E t h e r sAbstract: Novel structures of penta-crown ethers were successfully synthesized from trimethylolpropane triacrylate (TMPTA) with 2-aminomethyl crown ether; further reaction with 1-aza crown ethers, through Michael addition, furnished the newly synthesized host compounds of penta-crown ethers, which were characterized by 1 H NMR, 13 C NMR, and IR spectroscopy as well as FABMS and elemental analyses. The binding interaction of the new penta-crown ethers with alkali metal cations was studied through 1 H NMR spectroscopy and UV spectroscopy.Recently, there has been a growing interest in the chemistry of crown ethers, in particular in the design, synthesis, and study of abiotic receptors of multi-site crown ethers. Multi-site crown ethers have attracted considerable attention due to their fascinating structures and coordination properties with guest cations 1-12 and their application in synthetic, host-guest, and supramolecular chemistry. 13-20 A multi-site crown ether and some of its derivatives have found applications in quite widespread areas; their main application was their use as ionophores and host compounds.The binding behavior of crown ethers with alkali metal, alkaline metal, and organic cations 21,22 has been widely investigated. When the size of the cation exactly matches the cavity of the crown ether unit it always forms a 1:1 host/guest complex. The compounds that consist of more than two crown ether rings in the same molecule may produce intramolecular 'sandwich-type' complexes with the metal cations. When the cation size exceeds that of the crown ether unit cavity such as in the 'butterfly crown ethers', 23-26 it may form a host/guest 2:1 sandwich-type complex. [23][24][25][26][27][28][29][30][31] In our previous work, 17-20 we found an efficient synthetic approach to tris-, tetra-and penta-crown ethers by Michael addition using multi-acrylates as the linker. The triacrylate of trimethylolpropane triacrylate (TMPTA) has proven to be a useful linker to prepare multi-site crown ethers. This synthetic route was very effective and convenient. The novel host compounds containing multi-site crown ether rings are of great interest as they could form 1:n (n ≥ 3) host/guest complexes with metal cations.In order to further explore the synthesis and applications of the new multi-crown ethers, we chose TMPTA as the linker to synthesize a novel type of penta-crown ether. To our knowledge there is a scarcity of examples of pentacrown ethers reported. The structure of the newly synthesized penta-crown ethers is outlined in Figure 1. The new penta-crown ethers are expected to find applications in various areas, such as ligands for metal cations, and can be used as host compounds in the preparation of supramolecular assemblies in host-guest and supramolecular chemistry. The binding interaction of the synthesized pentacrown ethers with alkali metal cations was studied.