Host-guest complexes of nitro-substituted N-alkylbenzoaza-18-crowns-6

Abstract

A number of N-alkyl(nitrobenzo)aza-18-crowns-6 in which the nitrogen atom in the macroring is conjugated with the benzene ring were synthesized, and their complexing power was compared with that of model nitro derivatives of benzo-18-crown-6 and N-phenylaza-18-crown-6 using 1 H NMR spectroscopy and DFT/PBE quantum-chemical calculations. The stability constants of the complexes formed by crown ethers with NH 4 + , EtNH 3 + , Li + , Na + , and K + in CD 3 CN were determined by 1 H NMR titration. The complexing power of N-alkyl(nitrobenzo)aza-18-crowns-6 toward metal and ammonium cation was considerably higher than that of N-(4-nitrophenyl)aza-18-crown-6 and N-alkyl(nitrobenzo)aza-15-crown-5 and was comparable or higher than that of nitrobenzo-18-crown-6.Crown ethers are known to form stable host-guest complexes with metal ions, organic cations, and neutral polar molecules. The ability to form such complexes underlies application of crown ethers as selective ligands toward metal cations, in particular for extraction of metal ions, in ion-selective electrodes and light-sensitive systems, etc. [1-3]. Synthesis of aza crown compounds containing different numbers of nitrogen and oxygen atoms in the macroring attracts persistent interest [1][2][3]. From the viewpoint of potential application of aza crown compounds as structural fragments of light-sensitive ligands, specific attention is given to those possessing a nitrogen atom conjugated with a chromophore. Such compounds absorb light at considerably longer wavelengths as compared to common crown ether derivatives, which is especially important for photometric and fluorescent analysis, photocontrolled extraction, ion transport through membranes, and design of light-sensitive molecular devices. At present, phenyl aza crown ethers are used most widely for the above purposes; however, a considerable disadvantage is that their complex formation constants with metal ions are not high. In this respect, benzo-fused aza crown ethers may be appreciably more advantageous; on the other hand, derivatives of 1-aza-2,3-benzocrown ethers have been studied fairly poorly, and most their functional derivatives are almost inaccessible despite simple structure [3,4]. We previously developed a procedure for the synthesis of N-methyl benzo aza crown compounds with different sizes of the macroring (both unsubstituted at the benzene ring and formyl-substituted) [5-7] and nitro-

Complexation of bis‐crown stilbene with alkali and alkaline‐earth metal cations. Ultrafast excited state dynamics of the stilbene‐viologen analogue charge transfer complex

“…Similar low log K s values have been observed for the reaction of Li + with 4‐ N ‐tetraoxaaza‐15‐crown‐5 benzothiazole derivative and were attributed to metal ion coordination to only 4 oxygen atoms of the macrocycle, the remaining 2 vacancies in the lithium coordination sphere being filled by counter‐ion oxygen atoms and/or solvent molecules . A similar trend was identified in a study of complex formation of benzo‐18‐crown‐6 ether and N ‐phenylaza‐18‐crown‐6 ether derivatives with alkali metal cations . Apparently, in our case, too, the main cause of the low stability of Li + and Mg 2+ complexes of 1 is a sharp size mismatch between the cation and the 18‐crown‐6 ether cavity of 1 .…”

Evidence of electrochemical transduction of cation recognition by TEMPO derivatives

“…This spectroscopic study confirms the cation binding and agrees the selectivity and the K o values already reported in the literature. 24,25 ESI-MS measurements on compounds 1, 2 and 3 also confirm the cationic interactions with Ba 2+ , Ca 2+ and Na + by the presence of peaks corresponding to the cation adducts on the spectra.…”

N-Methylbenzoaza-18-crown-6-ether derivatives as efficient alkali metal cations sensors: the dipole moment and first hyperpolarizability

“…13,[17][18][19][20][21][22] It was reported that the Nalkyl derivatives of benzoaza-crown ethers, with nitrogen directly connecting to the benzene ring, are favourable for the formation of complexes with the metal and ammonium cations. 22,23 Recently, a series of novel 2-benzothiazole-, 4-pyridine-, and 2-and 4-quinoline-based styryl dyes containing an Nmethylbenzoaza-15(18)-crown-5(6)-ether moiety were synthesized, which have high performance as optical molecular sensors for alkali and alkaline-earth metal cations. 24 On the other hand, previous studies have demonstrated that cation recognition can be performed by probing the variation of the nonlinear optical (NLO) properties [25][26][27][28][29][30][31] such as the theoretical investigation on NLO molecular switches of spiropyran/merocyanine systems as selective cation sensors for alkali, alkaline earth, and transition metals.…”