Buzsáki Dániel, Kelemen Zsolt, Nyulászi László
Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szent Gellért tér 4, H-1111 Budapest, Hungary.
MTA-BME Computation Driven Chemistry Research Group, Szent Gellért tér 4, H-1111 Budapest, Hungary.
J Phys Chem A. 2020 Apr 2;124(13):2660-2671. doi: 10.1021/acs.jpca.0c00641. Epub 2020 Mar 24.
The stability and the structure of adducts formed between four substituted phosphanes (PX, X:H, F, Cl, and NMe) 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 (), 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 -type structures but carbene → phosphane adducts (-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 PCl, which has an extremely low energy LUMO in its T-shaped form. Although this PCl 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 and -type structures could be optimized, giving rise to bond-stretch isomerism. Likewise, for phosphorus ylides (), the stability of the adducts 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 (PX) are the most stable when X is electronegative, and the carbene is highly nucleophilic.
通过密度泛函理论（DFT）计算研究了四种取代膦（PX，X：H、F、Cl和NMe）与11种不同卡宾形成的加合物的稳定性和结构。在大多数情况下，加合物的结构强烈依赖于卡宾本身的稳定性，与加合物解离能的增加呈现线性关系。低稳定性的卡宾形成磷叶立德（），其可描述为通过一些反馈键支持的膦→卡宾加合物。具有高能量孤对电子的最稳定卡宾不会形成稳定的 -型结构，而是利用膦（带有电负性取代基）的低能量最低未占分子轨道（LUMO）形成卡宾→膦加合物（-型结构），这也得益于卡宾 - 磷族元素相互作用。特别值得注意的是PCl的情况，其T形结构具有极低能量的LUMO。尽管这种PCl结构是一个能量相当高的过渡态，但配合物的大稳定能使这种卡宾 - 膦加合物稳定。最有趣的是，对于中等稳定性的卡宾，和 -型结构都可以优化，从而产生键长异构体。同样，对于磷叶立德（），由低价磷卡宾（PX - 磷亚基）形成的加合物的稳定性与卡宾的稳定性呈线性关系。当X为电负性且卡宾具有高亲核性时，高价磷（PX）卡宾的加合物最稳定。
