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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A new look at the ylidic bond in phosphorus ylides and related compounds: Energy decomposition analysis combined with a domain-averaged fermi hole analysis
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A new look at the ylidic bond in phosphorus ylides and related compounds: Energy decomposition analysis combined with a domain-averaged fermi hole analysis

机译：磷酰基化物和相关化合物中的羟基键的新发现：能量分解分析与区域平均费米空穴分析相结合

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摘要

Geometries and bond dissociation energies of the ylide compounds H2CPH3, H2CPMe3, H2CPF3, (BH2)(2)CPH3, H2CNH3, H2CAsH3, H2SiPH3, and (BH2)(2)SiPH3 have been calculated using ab initio (MP2, CBS-QB3) and DFT (B3LYP, BP86) methods. The nature of the ylidic bond R2E1-(EX3)-X-2 was investigated with an energy decomposition analysis and with the domain-averaged Fermi hole (DAFH) analysis. The results of the latter method indicate that the peculiar features of the ylidic bond can be understood in terms of donor-acceptor interactions between closed-shell R2E1 and (EX3)-X-2 fragments. The DAFH analysis clearly shows that there are two bonding contributions to the ylidic bond. The strength of the donor and acceptor contributions to the attractive orbital interactions can be estimated from the energy decomposition analysis (EDA) calculations, which give also the contributions of the electrostatic attraction and the Pauli repulsion of the chemical bonding. The EDA and DAFH results clearly show that the orbital interactions take place through the singlet ground state of the R2E1 fragment where the donor orbital of E-1 yields pi-type back-donation while the (EX3)-X-2 lone-pair orbital yields sigma-type bonding. Both bonds are polarized toward (EX3)-X-2 when E-2 = P, while the sigma-type bonding remains more polarized at (EX3)-X-2 when E-2 = N, As. This shows that the phosphorus ylides exhibit a particular bonding situation which is clearly different from that of the nitrogen and arsenic homologues. With ylides built around a P-C linkage, the pi-acceptor strength of phosphorus and the sigma-acceptor strength at carbon contribute to a double bond which is enhanced by electrostatic contributions. The strength of the sigma and pi components and the electrostatic attraction are then fine-tuned by the substituents at C and P, which yields a peculiar type of carbon-phosphorus bonding. The EDA data reveal that the relative strength of the ylidic bond may be determined not only by the R2E1 -> (EX3)-X-2 pi back-donation, but also by the electrostatic contribution to the bonding. The calculations of the R2E1-(EX3)-X-2 bond dissociation energy using ab initio methods predict that the order of the bond strength is H2C-PMe3 > H2C-PF3 > H2C-PH3 > (BH2)(2)C-PH3 > H2C-AsH3 > H2C-NH3 similar to H2Si-PH3 similar to (BH2)(2)Si-PH3. The DFT methods predict a similar trend, but they underestimate the bond strength of (BH2)(2)CPH3.
机译：已使用从头算（MP3）和DFT（B3LYP，BP86）方法。通过能量分解分析和区域平均费米孔（DAFH）分析研究了R2E1-（EX3）-X-2分子键的性质。后一种方法的结果表明，可以根据闭壳R2E1和（EX3）-X-2片段之间的供体-受体相互作用来理解ylidic键的特殊特征。 DAFH分析清楚地表明，对ylidic键有两个键贡献。可以通过能量分解分析（EDA）计算来估算对吸引轨道相互作用的供体和受体的强度，该计算还给出了静电引力和化学键的保利排斥的贡献。 EDA和DAFH结果清楚地表明，轨道相互作用是通过R2E1片段的单峰基态发生的，其中E-1的供体轨道产生pi型背送，而（EX3）-X-2孤对轨道产生sigma型键合。当E-2 = P时，两个键都朝（EX3）-X-2极化，而当E-2 = N，As时，σ型键在（EX3）-X-2处保持更大极化。这表明磷的磷化物表现出特殊的结合状态，这明显不同于氮和砷同系物。使用围绕P-C键的内化物，磷的pi受体强度和碳处的sigma受体强度有助于形成双键，并通过静电作用增强该键。然后，通过C和P处的取代基对sigma和pi成分的强度以及静电引力进行微调，从而产生特殊类型的碳-磷键。 EDA数据表明，羟键的相对强度不仅可以通过R2E1->（EX3）-X-2 pi的背电荷来确定，还可以通过静电对键的贡献来确定。使用从头算方法计算R2E1-（EX3）-X-2键解离能可预测键强度的顺序为H2C-PMe3> H2C-PF3> H2C-PH3>（BH2）（2）C-PH3 > H2C-AsH3> H2C-NH3与类似于（BH2）（2）Si-PH3的H2Si-PH3类似。 DFT方法预测了类似的趋势，但它们低估了（BH2）（2）CPH3的键强度。

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