Roux Amandine, Nonat Aline M, Brandel Jérémy, Hubscher-Bruder Véronique, Charbonnière Loïc J
†Laboratoire d'Ingénierie Moléculaire Appliquée à l'Analyse and ‡Laboratoire de Reconnaissance et Procédés de Séparation Moléculaire, IPHC, UMR 7178 CNRS/UdS, IPHC, UMR 7178 CNRS/UdS, ECPM, Bât R1N0, 25 rue Becquerel, 67087 Strasbourg Cedex 02, France.
Inorg Chem. 2015 May 4;54(9):4431-44. doi: 10.1021/acs.inorgchem.5b00207. Epub 2015 Apr 13.
A family of 2,4-pyridyl-disubstituted bispidol derivatives bearing methylene carboxylic acid ethyl esters (L1-L3), methylene carboxylic acids (L4 and L5), or methylenethiophene (L6) groups were synthesized. In water, all ligands form rigid 1:1 complexes in the presence of Zn(II) in which the bicycle adopts a chair-chair conformation (cis isomer), as observed by (1)H NMR and, in the case of ligand L1, by an X-ray diffraction crystal structure. Interestingly, addition of Zn(II) ions on ligand L1 induces a metal-mediated selective hydrolysis of the ethyl esters. This selective hydrolysis was not observed upon addition of other cations such as Na(+), Mg(+), and Ca(2+). Reduction of the central ketone was achieved to prevent ring opening via retro Diels-Alder reactions and to afford highly stable and water-soluble ligands (L4, L5, L6). The complexation properties of L4 and L6 were studied in solution, with a particular interest for ligand L4. Fast complexation occurs in strongly acidic media (pH = 1), with a high affinity toward Cu(II) (log KCuL4 = 19.2(3), pCu = 17.0 at pH 7.4, pCu = -log[Cufree], [Cu] = 1 × 10(-6) M, [L] = 1 × 10(-5) M) and high selectivity versus Co(II), Ni(II), and Zn(II), as shown by the values of the binding constants obtained from potentiometric and spectrophotometric titrations. Reversible redox potential with E1/2 = -430 mV (vs normal hydrogen electrode) was measured. The complex was found to be fairly inert from acid-assisted dissociation experiments in 5 M HClO4 (t1/2 = 110 d at 25 °C).
合成了一族带有亚甲基羧酸乙酯（L1 - L3）、亚甲基羧酸（L4和L5）或亚甲基噻吩（L6）基团的2,4 - 吡啶基二取代双螺环衍生物。在水中，所有配体在Zn(II)存在下形成刚性的1:1配合物，其中双环采取椅 - 椅构象（顺式异构体），这通过(1)H NMR观察到，对于配体L1，还通过X射线衍射晶体结构观察到。有趣的是，在配体L1上添加Zn(II)离子会诱导乙酯的金属介导的选择性水解。添加其他阳离子如Na(+)、Mg(+)和Ca(2+)时未观察到这种选择性水解。通过还原中心酮来防止通过逆狄尔斯 - 阿尔德反应开环，并得到高度稳定且水溶性的配体（L4、L5、L6）。在溶液中研究了L4和L6的络合性质，特别关注配体L4。在强酸性介质（pH = 1）中发生快速络合，对Cu(II)具有高亲和力（log KCuL4 = 19.2(3)，在pH 7.4时pCu = 17.0，pCu = -log[Cufree]，[Cu] = 1×10(-6) M，[L] = 1×10(-5) M），并且相对于Co(II)、Ni(II)和Zn(II)具有高选择性，这通过电位滴定和分光光度滴定获得的结合常数的值表明。测量到可逆氧化还原电位E1/2 = -430 mV（相对于标准氢电极）。在5 M HClO4中进行的酸辅助解离实验表明该配合物相当惰性（在25°C下t1/2 = 110天）。
