Reaction of Germylene with Sulfur Dioxide: Gas-Phase Kinetic and Theoretical Studies

Time-resolved studies of germylene, GeH2, generated by laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene at 193 nm, have been carried out to obtain rate constants for its bimolecular reaction with SO2. The reaction was studied in the gas phase, mainly at a total pressure of 10 Torr (in SF6 bath gas) at five temperatures in the range 295–553 K. Pressure variation measurements over the range 1–100 Torr (SF6) at 295, 408, and 553 K revealed no pressure dependence. The second-order rate constants at 10 Torr (SF6 bath gas) fit the Arrhenius equation log­(k/cm3 molecule–1 s–1) = (−11.01 ± 0.09) + (4.62 ± 0.65 kJ mol–1)/RT ln 10, where the uncertainties are single standard deviations. The collisional efficiency is 19% at 298 K, and in kinetic terms the reaction resembles that of SiH2 with SO2 quite closely. Quantum chemical calculations at the B3LYP/aug-cc-pvQZ level suggest a mechanism occurring via the initial addition of GeH2 to one O atom of SO2 to form H2GeOSO which, via a 1,3-H shift followed by a cyclization, leads to a four-membered-ring species, cyclo-HGeO2SH­(cis)–. A low-energy H2 elimination results in the formation of cyclo-GeO2S, a hitherto unknown compound. A number of other species on the enthalpy surface have been identified, including the novel Ge­(OH)2···S, a cyclic five-membered ring comprising an S atom stabilized by dihydroxygermylene. However, none of these other molecules seem to be involved as intermediates in this reaction, either because barriers to their formation or rearrangement are too high or because their enthalpies are insufficiently negative for them to be collisionally stabilized under experimental conditions. The reaction is compared and contrasted with that of SiH2 + SO2.本研究通过193 nm激光闪光光解3,4-二甲基-1-锗杂环戊-3-烯制备得到锗烯（germylene, GeH₂），并对其开展时间分辨研究，以获取该物种与二氧化硫（SO₂）发生双分子反应的速率常数。反应于气相中进行，总压力主要控制在10 Torr（以六氟化硫（SF₆）为缓冲气体），实验温度覆盖295~553 K，共设置5个温度点。在295 K、408 K及553 K下，于1~100 Torr（SF₆）范围内开展压力依赖测试，结果显示反应速率无明显压力依赖性。在10 Torr（SF₆缓冲气体）条件下测得的二级速率常数符合阿伦尼乌斯（Arrhenius）方程：log(k/cm³ molecule⁻¹ s⁻¹) = (−11.01 ± 0.09) + (4.62 ± 0.65 kJ mol⁻¹)/RT ln 10，式中不确定度为单次标准偏差。298 K下该反应的碰撞效率为19%；从动力学层面而言，该反应与甲硅烯（silylene, SiH₂）和SO₂的反应极为相似。在B3LYP/aug-cc-pvQZ理论水平下开展的量子化学计算表明，反应机理为GeH₂首先加成至SO₂的一个氧原子，生成H₂GeOSO中间体；随后经1,3-氢迁移及环化过程，形成顺式四元环物种cyclo-HGeO₂SH⁻。经低能垒氢气消除过程，最终生成迄今尚未见报道的环-GeO₂S化合物。在焓势面上还鉴定出多种其他物种，包括新型Ge(OH)₂···S，即由硫原子与二羟基锗烯稳定形成的五元环物种。但上述物种均未作为该反应的中间体参与反应——要么是因为其形成或重排的能垒过高，要么是因为其焓变不足以负到可在实验条件下通过碰撞得以稳定存在。本研究还将该反应与SiH₂+SO₂的反应进行了对比与分析。