Metal-Mediated Synthesis of Antiaromatic Porphyrinoids from a BODIPY Precursor
Metal-Mediated Synthesis of Antiaromatic Porphyrinoids from a BODIPY Precursor
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DOI：
10.1002/anie.201006314
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Shinokubo, Hiroshi
中科院分区：
文献类型：
--
作者：
Sakida, Takafumi;Yamaguchi, Shigeru;Shinokubo, Hiroshi
卟啉类化合物在基础化学和应用化学中有着广泛的研究。卟啉类化合物的合成主要依赖于酸促进的吡咯缩合反应。[1]虽然金属介导的反应是当前合成化学中的一个强有力的工具，但它们很少用于合成卟啉类骨架。硼二吡咯（BODIPY）染料也受到了广泛关注的材料，如标记试剂，化学传感器，光捕获系统，染料敏化太阳能电池。[2]这两个重要的功能π-系统在结构上是相关的，但是从BODIPY前体合成卟啉类化合物在很大程度上仍然未被探索。脱氢轮烯不仅在大π-体系芳香性的基础研究方面，而且在超分子化学和材料科学领域都受到了长期的关注。[3]为了合成这些π-共轭大环，已经建立了基于过渡金属催化的交叉偶联反应的简便合成方法。大环中的亚乙炔基允许π共轭的延伸，并为高度有序的结构提供刚性。这些性质保证了具有独特结构和电子特征的大环的产生。在这里，我们报告的BODIPY单位纳入脱氢轮烯，提供稳定的反芳族卟啉类化合物通过transitionmetal介导的合成。[4]新的卟啉3的合成开始于通过Stille偶联将三甲基甲硅烷基乙炔基引入到α，α ′-二氯BODIPY 1中（方案1）。[5，6]通过在DMSO中与CuCl进行硅-Glaser偶联的直接同偶联提供了目标分子3，产率为沿着无环BODIPY低聚物（方案1）。[7]大环3与末端炔的Glaser偶联反应受到二乙炔基BODIPY的低溶解度的阻碍。大环3具有环状24π电子共轭。一般来说，4 n π卟啉类化合物呈现高度扭曲的结构，以避免由于反芳香性而导致的不稳定。[8]因此，通常需要精心设计以保持大环的平面性，以实现明显的反芳香性。[9]在3的情况下，刚性丁二炔连接基和BF 2单元应使整个大环成为扁平结构。事实上，单晶X射线衍射分析明确地阐明了3的平面和矩形结构，其平均平面偏差仅为0.058（图1）。[10]因此，通过NMR光谱分析证实了3的明显的反芳香性。在3的1H NMR谱中，δ= 5.01和4.53 ppm处的一组两个峰被指定为β-吡咯质子的信号，其与无环BODIPY 2（δ= 6.82和6.61 ppm）的信号相比显著上移，表明存在顺向环电流。顺向环电流效应还使内部BF 2部分的19 F信号向低场偏移（Δδ= 8.9 ppm）。此外，很大程度上正的核独立化学位移（NICS）[11]值（δ=+ 18.6 ppm）支持3的强反芳香性。此外，与BODIPY单体2 '（Ar=均三甲苯基）相比，3的反芳香性诱导了3中内消旋位置周围的大量键长交替，并且
Porphyrinoids have been extensively investigated both in fundamental and applied chemistry. The synthesis of porphyrinoids largely relies on the acid-promoted condensation reaction of pyrroles.[1] Although metal-mediated reactions are a powerful tool in current synthetic chemistry, they have rarely been employed for the synthesis of porphyrinoid skeletons. Boron dipyrrin (BODIPY) dyes have also received much attention for materials such as labeling reagents, chemosensors, light-harvesting systems, and dye-sensitized solar cells.[2] These two important functional π-systems are structurally related, but the synthesis of porphyrinoids from a BODIPY precursor has largely remained unexplored. Dehydroannulenes have received long-lasting attention in not only the basic aspect of aromaticity of large π-systems but also supramolecular chemistry and materials science.[3] For the synthesis of these π-conjugated macrocycles, facile synthetic methods have been established on the basis of transition-metal-catalyzed cross-coupling reactions. The ethynylene group in the macrocycles allows extension of π conjugation and offers rigidity for highly ordered structures. These properties promise the creation of macrocycles possessing unique structural and electronic features. Herein we report the incorporation of BODIPY units into dehydroannulenes to furnish stable antiaromatic porphyrinoids by transitionmetal-mediated synthesis.[4] The synthesis of novel porphyrinoid 3 was commenced with introduction of trimethylsilylethynyl groups to α, α’-dichloro BODIPY 1 via Stille coupling (Scheme 1).[5, 6] Direct homocoupling by sila-Glaser coupling with CuCl in DMSO provided the target molecule 3 in 27% yield along with acyclic BODIPY oligomers (Scheme1).[7] Normal Glaser coupling with terminal alkynes was hampered by the low solubility of diethynyl BODIPY after desilylation of 2.Macrocycle 3 can be considered to possess a cyclic 24πelectron conjugation. In general, 4nπ porphyrinoids take on highly distorted structures to avoid destabilization due to antiaromaticity.[8] Thus, elaboration to preserve the planarity of the macrocycle is often required to achieve distinct antiaromaticity.[9] In the case of 3, the rigid butadiyne linker and the BF2 unit should enforce the whole macrocycle into a flat structure. In fact, the single-crystal X-ray diffraction analysis unambiguously elucidated the planar and rectangular structure of 3, for which the mean plane deviation is only 0.058 (Figure 1).[10] Accordingly, distinct antiaromaticity of 3 was confirmed by NMR spectroscopic analysis. In the 1H NMR spectrum of 3, a set of two peaks at δ= 5.01 and 4.53 ppm was assigned as signals of the β-pyrrolic protons, which are significantly upfield-shifted in comparison to those of acyclic BODIPY 2 (δ= 6.82 and 6.61 ppm), indicating the existence of paratropic ring current. The paratropic ring current effect also shifts the 19F signal for the inner BF2 moiety downfield (Δδ= 8.9 ppm). In addition, the largely positive nucleus-independent chemical shift (NICS)[11] value (δ=+ 18.6 ppm) supports strong antiaromaticity of 3. Furthermore, antiaromaticity of 3 induced substantial bond length alternation around the meso position in 3 in comparison to BODIPY monomer 2’(Ar= mesityl) and the