N‐Methylbenzoazacrown ethers with the nitrogen atom conjugated with the benzene ring: the improved synthesis and the reasons for the high stability of complexes with metal and ammonium cations |
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Authors: | Sergey P Gromov Svetlana N Dmitrieva Artem I Vedernikov Nikolay A Kurchavov Lyudmila G Kuz'mina Yuri A Strelenko Michael V Alfimov Judith A K Howard |
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Institution: | 1. Photochemistry Centre, Russian Academy of Sciences, 7A Novatorov str., Moscow 119421, Russia;2. N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninskiy prosp., Moscow 119991, Russia;3. N. D. Zelinskiy Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninskiy prosp., Moscow 119991, Russia;4. Chemistry Department, Durham University, South Road, Durham DH1 3LE, UK |
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Abstract: | An improved method for the synthesis of formyl derivatives of N‐methylbenzoazacrown ethers is proposed. They are prepared in up to 68% yields over fewer steps and with a much shorter time required for the last step. The stability constants of complexes formed by N‐methylbenzoazacrown ethers and their structural analogs with alkali metal, alkaline‐earth metal and ammonium cations were determined by 1H NMR titration in CD3CN. High stability of complexes of N‐methyl derivatives of benzoazacrown ethers is demonstrated, comparable with or even exceeding the stability of benzocrown‐ether complexes and markedly exceeding the stability of complexes of phenylazacrown ethers with the same macrocycle size. The structures of azacrown ethers and their complexes with Ba(ClO4)2 were studied by X‐ray diffraction. A high degree of pre‐organization of N‐methylbenzoazacrown ethers toward the formation of complexes with metal and ammonium cations was noted, which is due to the clear‐cut pyramidal geometry of the nitrogen atom and the orientation of the lone electron pairs (LEPs) of most heteroatoms towards the centre of the macroheterocycle. Copyright © 2009 John Wiley & Sons, Ltd. |
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Keywords: | benzoazacrown ethers complex formation metal and ammonium cations stability |
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