Probing the Rotational Dynamics of meso-(2-Substituted)aryl Substituents in A2B-type Subporphyrins
Probing the Rotational Dynamics of meso-(2-Substituted)aryl Substituents in A2B-type Subporphyrins
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探讨 A2B 型亚卟啉中内消旋（2-取代）芳基取代基的旋转动力学
DOI：
10.1002/chem.201402778
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
and A. Osuka
中科院分区：
文献类型：
--
作者：
K. Yoshida;G. Copley;H. Mori;and A. Osuka
合成了A2B型B -甲氧基亚卟啉3 a -氨基和B -苯基亚卟啉7 a-c，e，含中（2 -取代）芳基取代基，并通过变温（VT）1H核磁共振光谱研究了它们的旋转动力学。在这些亚卟啉中，介芳基取代基的旋转受到合理安装的2取代基的阻碍。所确定的旋转势垒比先前报道的卟啉小得多。通过对旋转激活参数的比较，可知ΔG≠中ΔH≠和ΔS≠的贡献是可变的。亚卟啉3e、3f和7中甲基芳基取代基的2 -甲基和2 -乙基比2 -烷氧基取代基产生更大的旋转势垒。4‐二苄基的存在降低了3和7的旋转势垒，因为它具有稳定共面旋转过渡态的能力。与B -甲氧基亚卟啉相比，B -苯基亚卟啉的旋转势垒更小，这表明SN1型杂解对中芳基取代基旋转的贡献可以忽略不计。
A2B‐type B‐methoxy subporphyrins3 a–gand B‐phenyl subporphyrins7 a–c,e,gbearingmeso‐(2‐substituted)aryl substituents are synthesized, and their rotational dynamics are examined through variable‐temperature (VT)1H NMR spectroscopy. In these subporphyrins, the rotation ofmeso‐aryl substituents is hindered by a rationally installed 2‐substituent. The rotational barriers determined are considerably smaller than those reported previously for porphyrins. Comparison of the rotation activation parameters reveals a variable contribution of ΔH≠and ΔS≠in ΔG≠. 2‐Methyl and 2‐ethyl groups of themeso‐aryl substituents in subporphyrins3 e,3 f, and7 einduce larger rotational barriers than 2‐alkoxyl substituents. The rotational barriers of3 gand7 gare reduced by the presence of the 4‐dibenzylamino group owing to its ability to stabilize the coplanar rotation transition state electronically. The smaller rotational barriers found for B‐phenyl subporphyrins than for B‐methoxy subporphyrins indicate a negligible contribution of SN1‐type heterolysis in the rotation ofmeso‐aryl substituents.