Unusual aryl-porphyrin rotational barriers in peripherally crowded porphyrins.
Unusual aryl-porphyrin rotational barriers in peripherally crowded porphyrins.
复制标题
外围拥挤的卟啉中不寻常的芳基卟啉旋转屏障。
DOI：
10.1021/ic010958a
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
Shelnutt,JohnA
中科院分区：
文献类型：
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作者：
Medforth,CraigJ;Haddad,RaidE;Muzzi,CinziaM;Dooley,NealR;Jaquinod,Laurent;Shyr,DavidC;Nurco,DanielJ;Olmstead,MarilynM;Smith,KevinM;Ma,Jian-Guo;Shelnutt,JohnA
先前对5，10，15，20-四芳基卟啉的研究表明，势垒形成邻芳基-卟啉旋转（ΔG‡ROT）随核心取代基M的变化而变化，并且对于小金属（M = Ni）来说，与大金属（M = Zn）相比，以及对于阳离子（M = 4 H2+）与游离碱卟啉（M = 2 H）相比，该值较低。这归因于卟啉环的非平面畸变和由核心取代基引起的大环的可变形性的变化。在目前的工作中，X射线晶体学，分子力学（MM）计算，和变温（VT）1H NMR光谱被用来检查一些新的2，3，5，7，8，10，12，13，15，17，18，20-十二芳基卟啉（DArPs），特别是在一些5，10，15，20-四芳基-2，3，7，8，12，13，17，18-八苯基卟啉（TArOPPs），其中外围基团的空间拥挤总是导致非常非平面的大环。DArPs的X射线结构表明大环非平面构象随M的变化而存在差异，M = Zn、2 H或M = 4 H2+时观察到鞍形构象，M = Ni时观察到鞍形和/或褶边构象。VT NMR研究表明，质子化在TArOPPs中的作用是增加ΔG Δ ROT，这与在TArPs中观察到的作用相反，MM计算还预测当M = 4 H2+时，TArOPPs的势垒非常高。这些和其他发现表明，DArPs中的芳基-卟啉旋转势垒与大环沿着非平面畸变模式的变形性密切相关，该模式将被旋转的取代基移出卟啉平面。
Previous studies of 5,10,15,20-tetraarylporphyrins have shown that the barrier formesoaryl−porphyrin rotation (ΔG‡ROT) varies as a function of the core substituent M and is lower for a small metal (M = Ni) compared to a large metal (M = Zn) and for a dication (M = 4H2+) versus a free base porphyrin (M = 2H). This has been attributed to changes in the nonplanar distortion of the porphyrin ring and the deformability of the macrocycle caused by the core substituent. In the present work, X-ray crystallography, molecular mechanics (MM) calculations, and variable temperature (VT)1H NMR spectroscopy are used to examine the relationship between the aryl−porphyrin rotational barrier and the core substituent M in some novel 2,3,5,7,8,10,12,13,15,17,18,20-dodecaarylporphyrins (DArPs), and specifically in some 5,10,15,20-tetraaryl-2,3,7,8,12,13,17,18-octaphenylporphyrins (TArOPPs), where steric crowding of the peripheral groups always results in a very nonplanar macrocycle. X-ray structures of DArPs indicate differences in the nonplanar conformation of the macrocycle as a function of M, with saddle conformations being observed for M = Zn, 2H or M = 4H2+and saddle and/or ruffle conformations for M = Ni. VT NMR studies show that the effect of protonation in the TArOPPs is to increase ΔG‡ROT, which is the opposite of the effect seen for the TArPs, and MM calculations also predict a strikingly high barrier for the TArOPPs when M = 4H2+. These and other findings suggest that the aryl−porphyrin rotational barriers in the DArPs are closely linked to the deformability of the macrocycle along a nonplanar distortion mode which moves the substituent being rotated out of the porphyrin plane.