Improved Access to 1,8-Diformyl-carbazoles Leads to Metal-Free Carbazole-Based [2+2] Schiff Base Macrocycles with Strong Turn-On Fluorescence Sensing of Zinc(II) Ions
Improved Access to 1,8-Diformyl-carbazoles Leads to Metal-Free Carbazole-Based [2+2] Schiff Base Macrocycles with Strong Turn-On Fluorescence Sensing of Zinc(II) Ions
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DOI：
10.1021/acs.inorgchem.7b02763
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发表时间：
2018-03-05
影响因子：
4.6
通讯作者：
Brooker, Sally
中科院分区：
文献类型：
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作者：
Malthus, Stuart J.;Cameron, Scott A.;Brooker, Sally
报道了一种合成1,8-二甲酰咔唑3 （3a - 3,6-二叔丁基取代；3b - 3,6-未取代）的高产新路线。使用Heck偶联反应，然后进行臭氧分解，极大地促进了这些有趣的头单位的制备。对新一代希夫碱大环的初步探索已经打开了通往这些头单元(3)的通道，导致了从3a或3b直接（即无金属）合成两个[2 + 2]大环，分别用1,2-二氨基乙烷，1- 12l (tBu) （4a）和H2LH (4b)，以高收率（87-88%）获得黄色粉末。通过H2LH与醋酸锌（II）和三乙胺1:2:2反应，以83%的收率分离出二锌络合物[Zn2LH(OAc)(2)] （5b）。对醛3a和3b、大环H2LH和配合物[Zn2LH(OAc)(2)] （5b）进行了结构表征。咔唑nh3与两侧的1,8-二甲酰基团或H2LH与两侧的1,8-二亚胺基团形成分叉的氢键，形成扁平的全顺式构象。[Zn2LH(OAc)(2)]中保留了不含金属的大环H2LH的阶梯构象，尽管在两个三叉形口袋内两个锌（II）中心发生了去质子化和结合。锌离子的N3O2配位是由1 μ(1,1-)和1 μ(1,3-)一个桥接醋酸阴离子完成的。纳米摩尔[Zn2LH(OAc)(2)]在DMF中在335 nm激发可产生清晰可见的蓝色荧光（λ (max) = 460 nm）。对H2LH大环的进一步研究揭示了其开启荧光，具有选择性（超过Ca2+， Mg2+和一系列3d指示）和对锌（II）离子的纳摩尔灵敏度，突出了这些新的咔唑基希夫碱大环的许多潜在应用之一。
Development of a new and high yielding synthetic route to 1,8-diformyl-carbazoles 3 (3a 3,6-di-tertbutyl substituted; 3b 3,6-unsubstituted) is reported. Use of a Heck coupling reaction, followed by ozonolysis, has greatly facilitated the preparation of these interesting head units in useful quantities. An initial foray into the new generations of Schiff base macrocycles that ready access to these head units (3) opens up, has led to the direct (i.e., metal-free) synthesis of two [2 + 2] macrocycles from 3a or 3b with 1,2-diaminoethane, 1-12L(tBu) (4a) and H2LH (4b), respectively, obtained as yellow powders in high yields (87-88%). The dizinc complex [Zn2LH(OAc)(2)] (5b) was isolated as a bright yellow solid in 83% yield, by 1:2:2 reaction of H2LH with zinc(II) acetate and triethylamine. Aldehydes 3a and 3b, macrocycle H2LH, and complex [Zn2LH(OAc)(2)] (5b) have been structurally characterized. The carbazole NH makes bifurcated hydrogen bonds with the pair of flanking 1,8-diformyl-moieties in 3, or 1,8-diimine-moieties in H2LH, leading to a flat, all-cis conformation. The stepped conformation of the metal-free macrocycle H2LH is retained in [Zn2LH(OAc)(2)], despite deprotonation and binding of two zinc(II) centers within the two tridentate pockets. The N3O2 coordination of the zinc ions is completed by one mu(1,1-) and mu(1,3-) one bridging acetate anion. Excitation of nanomolar [Zn2LH(OAc)(2)] in DMF at 335 nm results in clearly visible blue fluorescence (lambda(max) = 460 nm). Further studies on the H2LH macrocycle revealed turn-on fluorescence, with selectivity (over Ca2+, Mg2+ and a range of 3d dications) and nanomolar sensitivity for zinc(II) ions, highlighting one of the many potential applications for these new carbazole-based Schiff base macrocycles.