Xu Zheng, Jin Juan, Li Zhifang, Qiu Huayu, Jiang Jianxiong, Lai Guoqiao, Kira Mitsuo
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Wenyi Road 222, Hangzhou 310012 (P.R. China), Fax: (+86) 571-28865135.
Chemistry. 2009 Aug 24;15(34):8605-8612. doi: 10.1002/chem.200901285.
Insertion reactions of dimethylsilylene (Me(2)Si:) into the silicon-chlorine bond of various substituted chlorosilanes have been computationally studied by using DFT calculations with a 6-31++G(d,p) basis set. All of the insertions investigated herein were exothermic (more than 40 kcal mol(-1)) and proceeded via three-membered cyclic transition states (TS) with one substituent of a chlorosilane in the ring plane and two other substituents out of the plane. Among the two possible concerted insertion pathways, the pathway via a TS with a silylene lone-pair orbital approaching a chlorosilane silicon atom was preferred. Important nucleophilic interactions of silylene lone-pair orbitals with anti-bonding sigma orbitals of Si-Y (in plane) were supported by carrying out a natural bond orbital (NBO) analysis of the reaction. A radical pathway through the initial abstraction of chlorine from chlorosilane by the silylene cannot compete with the preferred concerted pathway. Systematic calculations for SiMe(2) insertion into various chlorosilanes (YR(2)SiCl; Y (in-plane substituent) = H, Me, NH(2), OH, F, SiH(3), PH(2), SH and Cl; R (out-of-plane substituent) = H, Me, iPr and tBu) have revealed remarkable substituent effects on activation free energies (DeltaG(double dagger)). In-plane (Y) substituent effects were mostly electronic. Electron-withdrawing substituents accelerate the insertion through enhanced nucleophilic interaction between silylene lone-pair orbitals with the sigma*(Si-Y) orbital at the TS. The DeltaG(double dagger) values correlate with the sigma(I) constants as a scale of the inductive effect of Y. Out-of-plane (R) substituent effects are mainly steric, and bulky substituents increase the activation free energy . Correlation of the DeltaG(double dagger) values with Taft's steric substituent constants (E(s)) was observed. There was no significant difference in the out-of-plane substituent effects between the electron-withdrawing Cl and the electron-donating Me groups.
利用密度泛函理论（DFT）计算和6-31++G(d,p)基组，对二甲基硅烯（Me₂Si:）插入各种取代氯硅烷的硅-氯键的反应进行了计算研究。本文研究的所有插入反应都是放热的（超过40 kcal mol⁻¹），并且通过三元环过渡态（TS）进行，其中氯硅烷的一个取代基在环平面内，另外两个取代基在平面外。在两种可能的协同插入途径中，硅烯孤对轨道接近氯硅烷硅原子的TS途径是优选的。通过对反应进行自然键轨道（NBO）分析，证实了硅烯孤对轨道与Si-Y（平面内）反键σ轨道之间重要的亲核相互作用。硅烯从氯硅烷中最初夺取氯的自由基途径无法与优选的协同途径竞争。对SiMe₂插入各种氯硅烷（YR₂SiCl；Y（平面内取代基）=H、Me、NH₂、OH、F、SiH₃、PH₂、SH和Cl；R（平面外取代基）=H、Me、iPr和tBu）的系统计算揭示了取代基对活化自由能（ΔG‡）有显著影响。平面内（Y）取代基的影响主要是电子效应。吸电子取代基通过增强硅烯孤对轨道与过渡态下σ*(Si-Y)轨道之间的亲核相互作用来加速插入反应。ΔG‡值与σ(I)常数相关，作为Y诱导效应的尺度。平面外（R）取代基的影响主要是空间效应，体积大的取代基会增加活化自由能。观察到ΔG‡值与塔夫脱空间取代基常数（E(s)）之间的相关性。吸电子的Cl基团和供电子的Me基团在平面外取代基效应方面没有显著差异。
