ENHANCED NICKEL(II) CHELATION BY GEM-DIMETHYL-SUBSTITUTED MACROCYCLIC TETRATHIOETHERS
ENHANCED NICKEL(II) CHELATION BY GEM-DIMETHYL-SUBSTITUTED MACROCYCLIC TETRATHIOETHERS
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DOI：
10.1021/ja00023a013
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发表时间：
1991-11-06
影响因子：
15
通讯作者：
COOPER, SR
中科院分区：
文献类型：
--
作者：
DESPER, JM;GELLMAN, SH;COOPER, SR
比较了1，4，8，11-四硫代环十四烷（1）和在6-或6-和13-位（分别为2和3）具有偕二甲基对的衍生物的构象和Ni（II）结合性质。报道了2、3及其Ni（ClO_4）_2配合物的合成和晶体结构; 1及其Ni（BF_4）_2配合物的类似数据已在文献中发表了一段时间。所有三个镍（II）配合物显示非常相似的14元环构象，但无金属的大环显示不同的构象，在固态。这些结构数据表明，每个偕二甲基对逐步偏向大环的螯合构象。我们已经研究了相对Ni（II）的亲和力1-3在CD 3 NO2通过竞争实验监测H-1 NMR。在室温下，四硫醚2与Ni（II）的结合比1紧密约7.3倍，而3与Ni（II）的结合比1紧密约49倍。因此，每个偕二甲基对导致在这些条件下的Ni（II）结合自由能的1.1千卡/摩尔的改善。我们认为，在整个系列1-3的结合强度的增量改善与在无金属硫醚的晶体结构中观察到的大环构象的增量变化相关。
The conformational and Ni(II)-binding properties of 1,4,8,11-tetrathiocyclotetradecane (1) and derivatives bearing gem-dimethyl pairs at the 6- or at the 6- and 13-positions (2 and 3, respectively) are compared. The syntheses and crystal structures of 2, 3, and their Ni(ClO4)2 complexes are reported; analogous data for 1 and its Ni(BF4)2 complex have been in the literature for some time. All three Ni(II) complexes show very similar 14-membered ring conformations, but the metal-free macrocycles display different conformations, in the solid state. These structural data suggest that each gem-dimethyl pair progressively biases the macrocycle toward the chelating conformation. We have examined the relative Ni(II) affinities of 1-3 in CD3NO2 by means of competition experiments monitored by H-1 NMR. Tetrathioether 2 binds Ni(II) approximately 7.3 times more tightly than does 1 at room temperature, and 3 binds Ni(II) approximately 49 times more tightly than does 1. Thus, each gem-dimethyl pair leads to a 1.1 kcal/mol improvement in Ni(II) binding free energy under these conditions. We suggest that the incremental improvement in binding strength across the series 1-3 is correlated to the incremental changes in macrocycle conformation observed in the crystal structures of the metal-free thioethers.