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Selective Carriers of Ammonium Ions. 1. Synthesis and Template Effects of CsCl and X-ray Structure and Ionophoric Properties of Polyether Crowns Containing 1-Methyl-3,5-bis(methylene)-1H-pyrazole Units
A new series of asymmetric crown ethers of cyclic (7, 8) and acyclic structure (9) containing 1-methyl-3,5-bis(methylene)-1H-pyrazole units have been synthesized.Crowns 7 and 8 having 18 and 36 ring atoms have been obtained in 24percent and 25percent yields respectively by 1:1 and 2:2 cyclization of 1-methyl-3,5-bis(chloromethyl)-1H-pyrazole and disodium tetraethylene glycolate under the template effect of CsCl.When the Cs+ caution was not present in the above reaction, the crowns 7 and 8 were formed in lower yields.The X-ray structure of smaller crown 7 showed a flexible irregular cavity which presents an internal overall twist that changes the pseudo-2-fold axis of symmetry in the neighborhood of pyrazole ring into a pseudo mirror plane for the rest of it.A 1H and 13C NMR study has shown that in the Eu(fod)3-crown 7 complex, the pyrazolic sp2 nitrogen and the oxygens belonging to the polyether cavity are cooperatively acting as donor sites, the Eu+ being near the pyrazole side least hindered by the methyl group.The transport rates of alkali and ammonium ions are much higher for all polyether ligands 7-9 then for ester crowns 3 and 4 evaluated before.The larger crown, 8, is a selective carrier of NH4+ in relation to K+ and Na+ ions.However, the smaller crown, 7, and its acyclic analogue 9 (which shows a “plateau” selectivity toward NH4+ and alkali ions) are better carriers of K+ ions.
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Chiral Catalysts,
Chiral catalysts – SlideShare