Johnstone Timothy C, Briceno-Strocchia Alvaro I, Stephan Douglas W
Department of Chemistry , University of Toronto , 80 St. George Street , Toronto , Ontario M5S 3H6 , Canada.
Inorg Chem. 2018 Dec 17;57(24):15299-15304. doi: 10.1021/acs.inorgchem.8b02605. Epub 2018 Nov 29.
Proazaphosphatranes, also known as Verkade's superbases, are among the strongest nonionic bases available. Their extreme basicity derives in part from their ability to form a P-N transannulation upon interaction of the P atom with an electrophile. Although haloazaphosphatrane cations of the form [XP(RNCHCH)N] have previously been reported for X = Cl, Br, and I, no fluoroazaphosphatranes (X = F) have been prepared. Unlike treatment with Cl, Br, I, and surrogates thereof, reaction of proazaphosphatranes with XeF results in decomposition. Analysis of the decomposition products suggested that fluoride ions may be the destructive agent. However, oxidation of a proazaphosphatrane/BPh frustrated Lewis pair affords [FP(RNCHCH)N][FBPh]. Systematic trends in the experimental and computed NMR and structural data are considered. A computational analysis suggests that the transannular P-N distance varies as a result of the flexibility of the molecules and their capacity to deform in the solid state.
原氮磷杂环戊烷，也被称为韦尔卡德超强碱，是现有的最强非离子碱之一。它们的极端碱性部分源于磷原子与亲电试剂相互作用时形成P-N跨环结构的能力。尽管此前已报道过X = Cl、Br和I形式的卤代氮磷杂环戊烷阳离子，但尚未制备出氟代氮磷杂环戊烷（X = F）。与用Cl、Br、I及其替代物处理不同，原氮磷杂环戊烷与XeF反应会导致分解。对分解产物的分析表明氟离子可能是破坏剂。然而，原氮磷杂环戊烷/ BPh受阻路易斯酸碱对的氧化反应可得到[FP(RNCHCH)N][FBPh]。文中考虑了实验和计算得到的NMR及结构数据的系统趋势。计算分析表明，由于分子的柔韧性及其在固态下的变形能力，跨环P-N距离会发生变化。
