Stretching the P-C Bond. Variations on Carbenes and Phosphanes.,The Journal of Physical Chemistry A

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Stretching the P-C Bond. Variations on Carbenes and Phosphanes.
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2020-03-24 , DOI: 10.1021/acs.jpca.0c00641
Dániel Buzsáki ₁ , Zsolt Kelemen ₁ , László Nyulászi _{1,

2}

Affiliation

The stability and the structure of adducts formed between four substituted phosphanes (PX₃, X:H, F, Cl, and NMe₂) and 11 different carbenes have been investigated by DFT calculations. In most cases, the structure of the adducts depends strongly on the stability of the carbene itself, exhibiting a linear correlation with the increasing dissociation energy of the adduct. Carbenes of low stability form phosphorus ylides (F), which can be described as phosphane → carbene adducts supported with some back-bonding. The most stable carbenes, which have high energy lone pair, do not form stable F-type structures but carbene → phosphane adducts (E-type structure), utilizing the low-lying lowest unoccupied molecular orbital (LUMO) of the phosphane (with electronegative substituents), benefiting also from the carbene–pnictogen interaction. Especially noteworthy is the case of PCl₃, which has an extremely low energy LUMO in its T-shaped form. Although this PCl₃ structure is a transition state of rather high energy, the large stabilization energy of the complex makes this carbene–phosphane adduct stable. Most interestingly, in case of carbenes with medium stability both F- and E-type structures could be optimized, giving rise to bond-stretch isomerism. Likewise, for phosphorus ylides (F), the stability of the adducts G formed from carbenes with hypovalent phosphorus (PX—phosphinidene) is in a linear relationship with the stabilization of the carbene. Adducts of carbenes with hypervalent phosphorus (PX₅) are the most stable when X is electronegative, and the carbene is highly nucleophilic.

中文翻译：

延长 PC 债券。卡宾和磷烷的变体。

通过DFT计算研究了四种取代膦（PX ₃、X:H、F、Cl和NMe ₂ ）和11种不同卡宾之间形成的加合物的稳定性和结构。在大多数情况下，加合物的结构很大程度上取决于卡宾本身的稳定性，与加合物解离能的增加呈线性相关。低稳定性的卡宾形成磷叶立德（F），其可以被描述为由一些背键支撑的磷烷→卡宾加合物。最稳定的卡宾具有高能孤对电子，不会形成稳定的F型结构，而是利用膦的低位最低未占分子轨道（LUMO）形成卡宾→膦加合物（E型结构）（具有负电性）取代基），也受益于卡宾-磷元素相互作用。_{尤其值得注意的是 PCl 3}的情况，其 T 形形式的 LUMO 能量极低。虽然这种PCl ₃结构是相当高能量的过渡态，但配合物的大稳定能使得这种卡宾-膦加合物稳定。最有趣的是，对于中等稳定性的卡宾，F 型和E型结构都可以优化，从而产生键拉伸异构现象。同样，对于磷叶立德（F ），由卡宾与低价磷（PX-次膦亚基）形成的加合物G的稳定性与卡宾的稳定性呈线性关系。当X带负电时，卡宾与高价磷(PX ₅ )的加合物最稳定，并且卡宾具有高度亲核性。

更新日期：2020-03-24

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