Reversible Complexation of Ethylene by a Silylene under Ambient Conditions

Treatment
of toluene solutions of the silylenes Si­(SArMe6)2 (ArMe6 = C6H3-2,6­(C6H2-2,4,6-Me3)2, 1) or Si­(SArPri4)2 (ArPri4 = C6H3-2,6­(C6H3-2,6-Pri2)2, 2) with excess ethylene gas
affords the siliranes (ArMe6S)2SiCH2CH2 (3) or (ArPri4S)2SiCH2CH2 (4). Silirane 4 evolves
ethylene spontaneously at room temperature in toluene solution. A
Van’t Hoff analysis by variable-temperature 1H NMR
spectroscopy showed that ΔGassn =
−24.9(2.5) kJ mol–1 for 4. A
computational study of the reaction mechanism using a model silylene
Si­(SPh)2 (Ph = C6H5) was in harmony
with the Van’t Hoff analysis, yielding ΔGassn = −24 kJ mol–1 and an activation
energy ΔG⧧ = 54 kJ mol–1.

将硅烯（silylene）Si(SArMe₆)₂（其中ArMe₆为2,6-二(2,4,6-三甲基苯基)取代的苯基，对应化学式C₆H₃-2,6-(C₆H₂-2,4,6-Me₃)₂，记为化合物1）或Si(SArPri4)₂（其中ArPri4为2,6-二(2,6-二异丙基苯基)取代的苯基，对应化学式C₆H₃-2,6-(C₆H₃-2,6-Pri₂)₂，记为化合物2）的甲苯溶液与过量乙烯气体反应，可得到硅杂环丙烷（silirane）(ArMe₆S)₂SiCH₂CH₂（化合物3）或(ArPri4S)₂SiCH₂CH₂（化合物4）。硅杂环丙烷4在甲苯溶液中可于室温下自发释放乙烯。通过变温¹H核磁共振波谱法（variable-temperature ¹H NMR spectroscopy）开展的范特霍夫分析（Van’t Hoff analysis）显示，化合物4的缔合吉布斯自由能变ΔGassn为−24.9(2.5) kJ·mol⁻¹。采用模型硅烯Si(SPh)₂（其中Ph为苯基，对应化学式C₆H₅）对该反应机理开展的计算研究结果与前述范特霍夫分析一致，计算得到的ΔGassn为−24 kJ·mol⁻¹，活化吉布斯自由能ΔG⧧为54 kJ·mol⁻¹。