Nitro derivatives of N-alkylbenzoaza-15-crown-5: synthesis, structures, and complexation with metal and ammonium cations

Abstract

A number of N alkylnitrobenzoaza 15 crown 5 with the macrocycle N atom conjugated with the benzene ring were obtained. The structural and complexing properties of these com pounds were compared with those of model nitrobenzo and N (4 nitrophenyl)aza 15 crown 5 using X ray diffraction, 1 H NMR spectroscopy, and DFT calculations. The macrocy clic N atom of benzoazacrown ethers are characterized by a considerable contribution of the sp 3 hybridized state and a pronounced pyramidal geometry; the crownlike conforma tion of the macrocycle is preorganized for cation binding, which facilitates complexation. The stability constants of the complexes of crown ethers with the NH 4 + , EtNH 3 + , Na + , K + , Ca 2+ , and Ba 2+ ions were determined by 1 H NMR titration in MeCN d 3 . The most sta ble complexes were obtained with alkaline earth metal cations, which is due to the higher charge density at these cations. The characteristics of the complexing ability of N alkyl nitrobenzoaza 15 crown 5 toward alkaline earth metal cations are comparable with analo gous characteristics of nitrobenzo 15 crown 5 and are much better than those of N (4 nitrophenyl)aza 15 crown 5.

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

“…1, 2) is less intense due to longer distance between the interacting protons; however, that distance is shorter than 3.5 Å. Unlike 18-membered N-alkylbenzoazacrown ethers, their 15-membered analogs [9] displayed in the NOESY spectra cross peaks due to 3-H · · · R interactions (R is the substituent on the nitrogen), whereas interaction between 3-H and NCH 2 protons in the macroring is very weak. This means that the alkyl and alkoxy groups on the nitrogen atom in Ia-Id appear at similar distances from the ortho-proton (3-H) and that the above substituents deviate by similar distances from the benzene ring plane, i.e., the contribution of sp 3 -state of the nitrogen atom is considerable.…”

“…2, 1, 2). Approximately equal deviations of the N-substituents from the benzene ring in the complex may be presumed, which implies even larger contribution of sp 3 -hybridization of the nitrogen HOST-GUEST COMPLEXES OF NITRO-SUBSTITUTED N-ALKYLBENZOAZA-... [9], formed more stable complexes than those derived from phenylazacrown III. This indicates more rigid (and hence more suited to bind cations) structure of the macroring in ligands I and different contributions of the nitrogen atom in Ia-Id and III to complex formation.…”

“…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][6][7] and nitro-DOI: 10.1134/S1070428011070220 substituted N-alkylbenzoaza-15-crowns-5 via stepwise transformations of macroring in benzocrown ethers [8,9]. The developed synthetic approach to functionalized aza crown ether derivatives seems to be a promising alternative to the known methods of synthesis of 1-aza-2,3-benzocrown ethers [3,4].…”

“…It was found that increase in the length and degree of branching of the alkyl group in alkylamine is accompanied by reduction of the conversion of benzo-15-crown-5 into podands and that the complete conversion may be achieved by increasing the reaction time (due to the absence of side reactions) [11]. The resulting aza podands can be used for the synthesis of N-methylbenzoazacrown ethers such as Ia [8,12,13] and N-alkyl(nitrobenzo)-aza-15-crowns-5 [9] in which the nitrogen atom in the macroring is conjugated with the benzene ring. Following the proposed approach, in the present work we synthesized a series of N-alkyl(nitrobenzo)aza-18-crowns-6 (Scheme 2).…”

“…By heating The presence in molecules IVb-IVe of a secondary amino group and terminal hydroxy group made it possible to effect their intramolecular cyclization to previously unknown N-alkyl(nitrobenzo)azacrown ethers Ib-Ie (Scheme 2). Aza podand IVf having the bulkiest substituent on the nitrogen atom was not subjected to analogous transformations, taking into account unsuccessful attempt to obtain the corresponding product from 15-membered benzoazacrown ether [9]. To ensure successful cyclization of aza podands IVb-IVe to benzoazacrown ethers, the terminal hydroxy group therein should be replaced by a readily departing group or atom.…”