Controlling Tautomerization in Pyridine‐Fused Phosphorus‐Nitrogen Heterocycles
Controlling Tautomerization in Pyridine‐Fused Phosphorus‐Nitrogen Heterocycles
复制标题
控制吡啶-稠磷-氮杂环中的互变异构
DOI：
10.1002/chem.202200472
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Haley, Michael M.
中科院分区：
文献类型：
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作者：
McNeill, J. Nolan;Karas, Lucas J.;Bard, Jeremy P.;Fabrizio, Kevin;Zakharov, Lev N.;MacMillan, Samantha N.;Brozek, Carl K.;Wu, Judy I.;Johnson, Darren W.;Haley, Michael M.
磷-氮(PN)杂环的芳香族核心中包含第二个氮原子，导致意外的互变异构化为非芳香族形式。这种互变异构化最初是通过X射线结晶学在固体中观察到的，也可以用计算分析来解释。我们制备了一个在吡啶环上有一个氟的缺电子类似物(2 e)，结果表明弱碱性的吡啶阻止了互变异构化，这为转变发生的原因提供了关键的见解。为了研究溶液和固体杂环的区别，合成了锁定藜麦互变异构体的烷基化类似物，并研究了它们的1H核磁共振和UV/Vis光谱。最终，我们确定所有的杂环在溶液中都是芳香族互变异构体，而在固体中，除了2- 外，所有的杂环都切换到藜麦异构体。对这种转变的更好理解以及它在什么情况下发生，表明未来可以在可切换的开/关氢键导向受体中使用，这种受体可以调节为互补氢键。
Inclusion of a second nitrogen atom in the aromatic core of phosphorus‐nitrogen (PN) heterocycles results in unexpected tautomerization to a nonaromatic form. This tautomerization, initially observed in the solid state through X‐ray crystallography, is also explained by computational analysis. We prepared an electron deficient analogue (2 e) with a fluorine on the pyridine ring and showed that the weakly basic pyridine resisted tautomerization, providing key insights to why the transformation occurs. To study the difference in solution vs. solid‐state heterocycles, alkylated analogues that lock in the quinoidal tautomer were synthesized and their different1H NMR and UV/Vis spectra studied. Ultimately, we determined that all heterocycles are the aromatic tautomer in solution and all but2 eswitch to the quinoidal tautomer in the solid state. Better understanding of this transformation and under what circumstances it occurs suggest future use in a switchable on/off hydrogen‐bond‐directed receptor that can be tuned for complementary hydrogen bonding.