Department of Chemistry, Institute of Natural Sciences, Federal University of Lavras, MG, 37200-900, Lavras, Brazil.
Department of Chemistry, Institute of Exact Sciences, Federal University of Minas Gerais, MG, 31270-901, Belo Horizonte, Brazil.
Chemphyschem. 2022 Mar 4;23(5):e202100856. doi: 10.1002/cphc.202100856. Epub 2022 Jan 21.
Sulphur, not phosphorus, is the only known third-row element capable of experiencing an electrostatic gauche effect with fluorine. Some six-membered rings containing an endocyclic phosphorus atom and a β-fluorine substituent that can interconvert to axial (gauche relative to phosphorus) and equatorial positions were then analysed. While phosphines do not establish an electrostatic attraction between fluorine and phosphorus, some oxidised forms exhibit surprising stability for the sterically disfavoured axial orientation. Because the nature of this behaviour was not obvious, since an intramolecular hydrogen bond can appear, a phosphonium derivative was further studied and its axial conformation was found to be highly stable. A preference for the gauche arrangement appears even for the acyclic and sterically hindered (2-fluoroethyl)triphenylphosphonium cation. On the other hand, (ethane-1,2-diyl)bis(phosphonium) cations are exclusively in anti conformation due to an (+/+)-electrostatic repulsion between the positively charged phosphonium groups.
硫而非磷，是唯一已知的能经历静电 gauche 效应的第三周期元素，可以与氟相互作用。然后分析了一些含有一个中环磷原子和一个β-氟取代基的六元环，这些取代基可以相互转化为轴向（相对于磷 gauche）和赤道位置。虽然膦不能在氟和磷之间建立静电吸引，但一些氧化形式表现出对空间不利的轴向位置的惊人稳定性。由于这种行为的性质不明显，因为可能会形成分子内氢键，因此进一步研究了一种磷翁衍生物，发现其轴向构象非常稳定。即使对于非环状和空间位阻较大的（2-氟乙基）三苯基膦阳离子，gauche 排列也表现出偏好。另一方面，（乙烷-1,2-二基）双（磷翁）阳离子由于正电荷磷翁基团之间的（+ / +）-静电排斥而仅处于反式构象。
