Alkali metal cation-π interactions observed by using a lariat ether model system

被引:129
作者
Meadows, ES
De Wall, SL
Barbour, LJ
Gokel, GW [1 ]
机构
[1] Washington Univ, Sch Med, Bioorgan Chem Program, St Louis, MO 63110 USA
[2] Washington Univ, Sch Med, Dept Mol Biol & Pharmacol, St Louis, MO 63110 USA
[3] Univ Missouri, Dept Chem, Columbia, MO 65211 USA
关键词
D O I
10.1021/ja003059e
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The Na+ or K+ cation-pi interaction has been experimentally probed by using synthetic receptors that comprise diaza-18-crown-6 lariat ethers having ethylene sidearms attached to aromatic pi -donors. The side chains are 2-(3-indolyl)ethyl (7), 2-(3-(1-methyl)indolyl)ethyl (8), 2-(3-(5-methoxy)indolyl)ethyl (9), 2-(4-hydroxyphenyl)ethyl (10). 2-phenylethyl (11), 2-pentafluorophenylethyl (12), and 2-(1-naphthyl)ethyl (13). Solid-state structures are reported for six examples of alkali metal complexes in which the cation is pi -coordinated by phenyl, phenol, or indole. Indole-containing crown, 7, adopts a similar conformation when bound by NaI, KI, KSCN, or KPF6. In each case, the macroring and both arenes coordinate the cation: the counteranion is excluded from the solvation sphere. NMR measurements in acetone-d(6) solution confirm the observed solid-state conformations of unbound 7 and 7 . NaI. In 7 . Na+ and 7 .K+, the pyrrolo, rather than benzo, subunit of indole is the pi -donor for the alkali metal cation. Cation-pi complexes were also observed fur 10 . KI and 11 KI. In these cases, the orientation of the cation on the aromatic ring is in accord with the binding site predicted by computational studies. In contrast to the phenyl case (11) the pentafluorophenyl group of 12 failed to coordinate K+. Solid-state structures are also reported for 7 . NaPF6, 10 . NaI, 11 . NaI, 13 . KI, 13 . KPF6, and 9 NaI, in which cation-pi complexation is not observed. Steric and electrostatic considerations in the pi -complexation of alkali metal cations by these lariat ethers are thought to account fur the observed complexation behavior or lack thereof.
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页码:3092 / 3107
页数:16
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