Treatment of PCl[N(SiMe3)2](NPri2)
(1) with potassium–graphite in thf afforded the colourless, crystalline diphosphine P[N(SiMe3)2](NPri2)}2
(2) in good yield. Sublimation of 2in vacuo yielded the yellow phosphinyl radical P[N(SiMe3)2](NPri2)
(3), which upon cooling reverted to 2; the latter in C6D6 at 298 K was a mixture of rac and meso diastereoisomers. The yellow, crystalline phosphenium salt P[N(SiMe3)2](NPri2)}[AlCl4]
(4) was obtained from 1 and ½Al2Cl6 in CH2Cl2. By single-crystal X-ray diffraction (XRD) the structures of the known compound 1 and of 2 and 4 were determined. The structure of the radical 3, formed by the thermal homolytic dissociation of the diphosphine 2, was determined in the gas phase by electron diffraction (GED), utilising data from UMP2/6-31+G*
ab initio calculations. The model of the molecule in the GED structure analysis was described by a set of internal coordinates and an initial set of Cartesian coordinates from ab initio calculations, facilitating the structure analysis. The experimental data were found to be consistent with the presence of a single conformer of the radical in the gas phase. The computed standard homolytic dissociation enthalpy of the P–P bond in the corresponding diphosphine 2, corrected for BSSE, 54 kJ mol−1, is substantially reduced compared to the dissociation enthalpy of tetramethyldiphosphine by the reorganisation energies of the fragments that form upon dissociation. The intrinsic energy content of the P–P bond in the diphosphine 2 was estimated to be 286 kJ mol−1, in agreement with the results of previous work on a series of crowded diphosphines.
将 PCl[N(SiMe3)2](NPri2)(1)与石墨
钾在 thf 中处理,可得到无色结晶的
二膦 P[N(SiMe3)2](NPri2)}2 (2),收率很高。2 在真空中升华得到黄色膦基 P[N(SiMe3)2](NPri2)(3),冷却后还原成 2;后者在 298 K 的 C6D6 中是 rac 和中间非对映异构体的混合物。从 1 和 ½
Al2Cl6 在
CH2Cl2 中得到黄色结晶膦盐 P[N(SiMe3)2](NPri2)}[AlCl4] (4)。通过单晶 X 射线衍射 (XRD),确定了已知化合物 1 以及 2 和 4 的结构。利用
UMP2/6-31+G* ab initio 计算的数据,通过电子衍射 (GED) 确定了
二膦 2 热均解形成的自由基 3 在气相中的结构。GED 结构分析中的分子模型是由一组内部坐标和一组来自 ab initio 计算的初始笛卡尔坐标描述的,这为结构分析提供了便利。实验数据表明,该自由基在气相中存在单一构象。计算得出的相应
二膦 2 中 P-P 键的标准同解离焓(根据 BS
SE 修正)为 54 kJ mol-1,与四甲基
二膦的离焓相比,离解时形成的碎片的
重组能大大降低了离焓。据估计,
二膦 2 中 P-P 键的固有能量含量为 286 kJ mol-1,这与之前对一系列拥挤
二膦的研究结果一致。