Brydon Samuel C, Lim Shea Fern, Khairallah George N, Maître Philippe, Loire Estelle, da Silva Gabriel, O'Hair Richard A J, White Jonathan M
Accurate Mass Scientific Pty Ltd , P.O. Box 92, Keilor , VIC 3036 , Australia.
Laboratoire de Chimie Physique (UMR8000), Université Paris-Sud, CNRS , Université Paris Saclay , Orsay 91405 , France.
J Org Chem. 2019 Aug 16;84(16):10076-10087. doi: 10.1021/acs.joc.9b01264. Epub 2019 Aug 2.
Ion-molecule reactions between thiiranium ion ( 213) and cyclohexene and -cyclooctene resulted in the formation of addition products and ( 295 and 323, respectively) via an electrophilic addition pathway. Associative π-ligand exchange involving direct transfer of the PhS moiety, which has been observed for analogous seleniranium ions in the gas phase, did not occur despite previous solution experiments suggesting it as a valid pathway. DFT calculations at the M06-2X/def2-TZVP level of theory showed high barriers for the exchange reaction, while the addition pathway was more plausible. Further support for this pathway was provided with Hammett plots showing the rate of reaction to increase as the benzylic position of thiiranium ion derivatives became more electrophilic (ρ = +1.69; = 0.974). The more reactive isomeric sulfonium ion was discounted as being responsible for the observed reactivity with infrared spectroscopy and DFT calculations suggesting little possibility for isomerization. To further explore the differences in reactivity, thiiranium ion and sulfonium ion were formed independently, with the latter ion reacting over 260 times faster toward -cyclooctene than the thiiranium ion rationalized by calculations suggesting a barrierless pathway for sulfonium ion to react with the cycloalkene.
硫鎓离子（213）与环己烯和环辛烯之间的离子 - 分子反应通过亲电加成途径生成了加成产物（分别为295和323）。尽管之前的溶液实验表明涉及PhS部分直接转移的缔合π配体交换是一种有效的途径，但在气相中对类似的硒鎓离子观察到的这种交换反应并未发生。在M06 - 2X/def2 - TZVP理论水平上的密度泛函理论（DFT）计算表明交换反应具有高势垒，而加成途径更合理。哈米特（Hammett）图进一步支持了该途径，该图表明随着硫鎓离子衍生物的苄基位置亲电性增强，反应速率增加（ρ = +1.69；R² = 0.974）。反应活性更高的异构硫鎓离子被排除是观察到的反应性的原因，红外光谱和DFT计算表明异构化的可能性很小。为了进一步探索反应性的差异，硫鎓离子（213）和硫鎓离子分别独立形成，计算表明后者离子与环辛烯的反应速度比硫鎓离子快260倍以上，这表明硫鎓离子与环烯烃反应存在无势垒途径。
