Dransfeld Alk, Nyulászi László, Schleyer Paul von Ragué
Computer Chemistry Center, Institut für Organische Chemie, Universität Erlangen-Nürnberg, Henkestrasse 42, D-91054 Erlangen, Germany.
Inorg Chem. 1998 Aug 24;37(17):4413-4420. doi: 10.1021/ic971385y.
The aromaticity of phospholes, P(n)()(CH)(4)(-)(n)()PH with n = 0-4, becomes larger as the number of dicoordinate atoms (n) in the ring increases. This is due to the decreasing pyramidality of the tricoordinate phosphorus. The aromaticity is shown by various criteria, e.g., the nucleus-independent chemical shifts (NICS), and the separated pi contribution NICS(pi), as well as the Bird aromaticity (BI) and the bond-shortening (BDSHRT) indexes. The change of the aromaticity is correlated with the bond angle sum (the degree of planarity) about the tricoordinate phosphorus (e.g., correlation coefficient = 0.968 with NICS). The aromaticities of the planar P(n)()(CH)(4)(-)(n)()PH phospholes (first-order saddle points for n = 0-3, minimum for n = 4) (NICS values between -15.4 and -17.4 ppm) all are similar. The same is true for the NICS (-12.3 to -15.9) aromaticity of the phospholyl anions (P(n)()(CH)(4)(-)(n)()P-), n = 0-4, which are close to those of the planar phospholes. According to NICS, BI and BDSHRT planar phospholes are more aromatic than pyrrol or thiophene. Isodesmic reaction energies do not correlate with the bond angle sum, since the energy cost of the increasing planarization of the tricoordinate phosphorus consumes the stabilization achieved by aromaticity.
磷杂环戊二烯（P(n)()(CH)(4)(-)(n)()PH，n = 0 - 4）的芳香性随着环中二配位原子（n）数量的增加而增强。这是由于三配位磷的锥角减小所致。芳香性通过多种标准来体现，例如，核独立化学位移（NICS）、分离的π贡献NICS(π)，以及伯德芳香性（BI）和键长缩短（BDSHRT）指数。芳香性的变化与围绕三配位磷的键角总和（平面度）相关（例如，与NICS的相关系数 = 0.968）。平面P(n)()(CH)(4)(-)(n)()PH磷杂环戊二烯（n = 0 - 3时为一阶鞍点，n = 4时为最小值）的芳香性（NICS值在 - 15.4至 - 17.4 ppm之间）都相似。磷杂环戊二烯基阴离子（P(n)()(CH)(4)(-)(n)()P - ），n = 0 - 4的NICS（ - 12.3至 - 15.9）芳香性也是如此，其与平面磷杂环戊二烯的芳香性相近。根据NICS、BI和BDSHRT，平面磷杂环戊二烯比吡咯或噻吩更具芳香性。等键反应能量与键角总和不相关，因为三配位磷平面化增加的能量消耗了芳香性所带来的稳定性。
