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Al(ORF)3 (RF = C(CF3)3) activated silica: a well-defined weakly coordinating surface anion
Chemical Science ( IF 7.6 ) Pub Date : 2019/12/19 , DOI: 10.1039/c9sc05904k Damien B Culver 1 , Amrit Venkatesh 2 , Winn Huynh 1 , Aaron J Rossini 2 , Matthew P Conley 1
Chemical Science ( IF 7.6 ) Pub Date : 2019/12/19 , DOI: 10.1039/c9sc05904k Damien B Culver 1 , Amrit Venkatesh 2 , Winn Huynh 1 , Aaron J Rossini 2 , Matthew P Conley 1
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Weakly Coordinating Anions (WCAs) containing electron deficient delocalized anionic fragments that are reasonably inert allow for the isolation of strong electrophiles. Perfluorinated borates, perfluorinated aluminum alkoxides, and halogenated carborane anions are a few families of WCAs that are commonly used in synthesis. Application of similar design strategies to oxide surfaces is challenging. This paper describes the reaction of Al(ORF)3*PhF (RF = C(CF3)3) with silica partially dehydroxylated at 700 °C (SiO2-700) to form the bridging silanol ![[triple bond, length as m-dash]](https://www.rsc.org/images/entities/char_e002.gif)
Si–OH⋯Al(ORF)3 (1). DFT calculations using small clusters to model 1 show that the gas phase acidity (GPA) of the bridging silanol is 43.2 kcal mol−1 lower than the GPA of H2SO4, but higher than the strongest carborane acids, suggesting that deprotonated 1 would be a WCA. Reactions of 1 with NOct3 show that 1 forms weaker ion-pairs than classical WCAs, but stronger ion-pairs than carborane or borate anions. Though 1 forms stronger ion-pairs than these state-of-the-art WCAs, 1 reacts with alkylsilanes to form silylium type surface species. To the best of our knowledge, this is the first example of a silylium supported on derivatized silica.
中文翻译：
Al(ORF)3 (RF = C(CF3)3) 活化二氧化硅：定义明确的弱配位表面阴离子
弱配位阴离子 (WCA) 包含合理惰性的缺电子离域阴离子片段，可用于分离强亲电试剂。全氟化硼酸盐、全氟化铝醇盐和卤代碳硼烷阴离子是合成中常用的几个 WCA 家族。将类似的设计策略应用于氧化物表面具有挑战性。本文介绍了 Al(OR F ) 3 *PhF (R F = C(CF 3 ) 3 ) 与在 700 ℃ 部分脱羟基的二氧化硅 (SiO 2-700 ) 反应形成桥连硅烷醇Si-OH⋯Al(或F ) 3 ( 1）。使用小簇对模型1进行的DFT 计算表明，桥接硅烷醇的气相酸度 (GPA)比 H 2 SO 4的 GPA 低 43.2 kcal mol -1，但高于最强的碳硼烷酸，这表明去质子化的1会成为 WCA。1与 NOct 3的反应表明，1形成比经典 WCA 更弱的离子对，但比碳硼烷或硼酸根阴离子形成更强的离子对。虽然1形成的离子对比这些最先进的 WCA 更强，但1与烷基硅烷反应形成甲硅烷型表面物质。据我们所知，这是第一个以衍生二氧化硅为载体的甲硅烷基的例子。
更新日期：2020-02-13
Si–OH⋯Al(ORF)3 (1). DFT calculations using small clusters to model 1 show that the gas phase acidity (GPA) of the bridging silanol is 43.2 kcal mol−1 lower than the GPA of H2SO4, but higher than the strongest carborane acids, suggesting that deprotonated 1 would be a WCA. Reactions of 1 with NOct3 show that 1 forms weaker ion-pairs than classical WCAs, but stronger ion-pairs than carborane or borate anions. Though 1 forms stronger ion-pairs than these state-of-the-art WCAs, 1 reacts with alkylsilanes to form silylium type surface species. To the best of our knowledge, this is the first example of a silylium supported on derivatized silica.
中文翻译：
Al(ORF)3 (RF = C(CF3)3) 活化二氧化硅：定义明确的弱配位表面阴离子
弱配位阴离子 (WCA) 包含合理惰性的缺电子离域阴离子片段，可用于分离强亲电试剂。全氟化硼酸盐、全氟化铝醇盐和卤代碳硼烷阴离子是合成中常用的几个 WCA 家族。将类似的设计策略应用于氧化物表面具有挑战性。本文介绍了 Al(OR F ) 3 *PhF (R F = C(CF 3 ) 3 ) 与在 700 ℃ 部分脱羟基的二氧化硅 (SiO 2-700 ) 反应形成桥连硅烷醇
Si-OH⋯Al(或F ) 3 ( 1）。使用小簇对模型1进行的DFT 计算表明，桥接硅烷醇的气相酸度 (GPA)比 H 2 SO 4的 GPA 低 43.2 kcal mol -1，但高于最强的碳硼烷酸，这表明去质子化的1会成为 WCA。1与 NOct 3的反应表明，1形成比经典 WCA 更弱的离子对，但比碳硼烷或硼酸根阴离子形成更强的离子对。虽然1形成的离子对比这些最先进的 WCA 更强，但1与烷基硅烷反应形成甲硅烷型表面物质。据我们所知，这是第一个以衍生二氧化硅为载体的甲硅烷基的例子。
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