NH Tautomerism of a Quadruply Fused Porphyrin: Rigid Fused Structure Delays the Proton Transfer
NH Tautomerism of a Quadruply Fused Porphyrin: Rigid Fused Structure Delays the Proton Transfer
复制标题
四重稠合卟啉的 NH 互变异构：刚性稠合结构延迟质子转移
DOI：
10.1021/acs.jpcb.7b10945
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发表时间：
2017
影响因子：
3.3
通讯作者：
Takahiko Kojima
中科院分区：
文献类型：
--
作者：
5.Yuta Saegusa;Tomoya Ishizuka*;Yoshihito Shiota;Kazunari Yoshizawa;Takahiko Kojima
本文报道了一种四重稠合卟啉衍生物（H2 QFP-Mes，3）的NH互变异构现象，它在非稠合吡咯的一个β-位上有一个mesityl基团以降低结构对称性，使我们能够用1HNMR光谱观察NH互变异构现象。化合物3的两个非稠合吡咯上有两个内部的NH质子，在不同氘代溶剂中的变温1H NMR实验证明了3的NH互变异构。VT-NMR研究表明，3的NH互变异构的活化能垒比四苯基卟啉的大。NH互变异构体的正活化熵（ΔS ε = 89 J mol-1 K-1）可以用基态3的π-π堆积二聚体结构的解离来解释，这一点已被晶体结构和NMR测量所证实.在动力学研究和密度泛函理论计算的基础上，详细讨论了3的NH互变异构中间体的稳定性和过渡态。
We report herein NH tautomerism of a freebase derivative of a quadruply fused porphyrin (H2QFP-Mes,3), which has one mesityl group at one of the β-positions of the nonfused pyrroles to lower the structural symmetry, allowing us to observe the NH tautomerism with1H NMR spectroscopy. Compound3was revealed to have the two inner NH protons on the two nonfused pyrroles, and the NH tautomerism of3was evidenced by variable-temperature (VT)1H NMR experiments in various deuterated solvents. The VT-NMR studies revealed that the activation barrier for the NH tautomerism of3was larger than that of tetraphenylporphyrin. The positive activation entropy (ΔS‡= 89 J mol–1K–1), determined for the NH tautomerism, can be explained by dissociation of the π–π stacked dimer structure of3in the ground state, as evidenced by the crystal structure and NMR measurements. On the basis of the kinetic studies and density functional theory calculations, the stability of intermediates in the NH tautomerism of3and the transition states have been discussed in detail.