Ueta Yasuhiro, Mikami Koichi, Ito Shigekazu
Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology , 2-12-1, Ookayama, Meguro, Tokyo 152-8552, Japan.
Inorg Chem. 2015 Sep 8;54(17):8778-85. doi: 10.1021/acs.inorgchem.5b01399. Epub 2015 Aug 27.
Heteroaryl-substituted air-tolerant 2,4-bis(2,4,6-tri-t-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyls in the open-shell singlet state were synthesized by a sterically promoted regioselective S(N)Ar process. Here we demonstrate that these diyls are effective for capturing hydrogen fluoride (HF) generated by intermediary base-coordinated HF and amine-stabilized HF reagents. The hydrofluorination reaction predominantly occurred on the λ(3)σ(3)-phosphorus atoms to afford the energetically disfavored 1λ(5),3λ(5)-diphosphete. The positively charged t-butyl-substituted phosphorus atom trapped the fluoride anion, and the subsequent protonation was controlled by the steric effect. X-ray crystallographic analysis and an Atoms in Molecule study of the air-stable 1λ(5),3λ(5)-diphosphete bearing P-H and P-F bonds revealed that the delocalized ylidic linkages in the four-membered ring were almost identical, in contrast to the nonsymmetrically substituted 2,4-bis(2,4,6-tri-t-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl. Hydrofluorination efficiently induced a remarkable exchange of visible photoabsorption. The charge-transfer-type transition from highest occupied molecular orbital to lowest unoccupied molecular orbital was highly tuned, which is advantageous for the facile identification of HF. In contrast to hitherto known trapping reagents for HF based on cleavage of the H-F bond, several hydrofluorinated P-heterocycles were reconverted into the 1,3-diphosphacyclobutane-2,4-diyl by treatment with sodium hydride. However, in the hydrofluorination of the benzoyl-substituted 1,3-diphosphacyclobutane-2,4-diyl, fluorination and protonation occurred at the t-butyl-substituted phosphorus atom and the skeletal carbon atom, respectively, and the energetically preferable 1λ(5),3λ(3)-dihydrodiphosphete was isolated as a purple-blue crystalline compound. These findings are promising not only for the practical detection of HF but also for the development of fluorine technology based on the chemistry of phosphorus heterocycles.
通过空间位阻促进的区域选择性S(N)Ar过程合成了处于开壳单重态的杂芳基取代的耐空气2,4-双(2,4,6-三叔丁基苯基)-1,3-二磷杂环丁烷-2,4-二基。在此，我们证明这些二基对于捕获由中间碱配位的HF和胺稳定的HF试剂产生的氟化氢(HF)是有效的。氢氟化反应主要发生在λ(3)σ(3)-磷原子上，得到能量上不利的1λ(5),3λ(5)-二磷杂环戊二烯。带正电荷的叔丁基取代的磷原子捕获氟阴离子，随后的质子化受空间效应控制。对含有P-H和P-F键的空气稳定的1λ(5),3λ(5)-二磷杂环戊二烯进行X射线晶体学分析和分子中的原子研究表明，与非对称取代的2,4-双(2,4,6-三叔丁基苯基)-1,3-二磷杂环丁烷-2,4-二基相比，四元环中离域的叶立德键几乎相同。氢氟化有效地诱导了可见光吸收的显著变化。从最高占据分子轨道到最低未占据分子轨道的电荷转移型跃迁得到了高度调节，这有利于HF的简便识别。与迄今已知的基于H-F键断裂的HF捕获试剂不同，几种氢氟化的P-杂环化合物通过用氢化钠处理可重新转化为1,3-二磷杂环丁烷-2,4-二基。然而，在苯甲酰基取代的1,3-二磷杂环丁烷-2,4-二基的氢氟化反应中，氟化和质子化分别发生在叔丁基取代的磷原子和骨架碳原子上，能量上更有利的1λ(5),3λ(3)-二氢二磷杂环戊二烯被分离为紫蓝色结晶化合物。这些发现不仅对HF的实际检测有前景，而且对基于磷杂环化学的氟技术的发展也有前景。
