Li⁺-Induced σ-Bond Metathesis: Aryl for Methyl Exchange on Boron in a Methylated Monocarbadodecaborate Anion

At 190 °C, formal σ-bond metathesis between the B−CH3 bond in position 12 of the lithium monocarbadodecaborate derivative 1a and the C−Si(CH3)3 bond in p-bromophenyltrimethylsilane occurs and produces Si(CH3)4 and a salt of the arylated carborate anion 2, whose X-ray structure has been determined. The reaction requires the presence of active Li+ cations and does not occur with the cesium salt 1b or when 12-crown-4 is added to 1a. Possible mechanisms are briefly discussed.在190 ℃条件下，单碳十二硼酸盐锂衍生物1a的12位B−CH₃键与对溴苯基三甲基硅烷中的C−Si(CH₃)₃键发生形式σ键复分解反应，生成四甲基硅烷（Si(CH₃)₄）与芳基化碳硼烷阴离子2的盐，该产物的X射线晶体结构已被解析确定。该反应需活性锂离子参与，使用铯盐1b或向1a中添加12-冠-4时，反应均无法进行。本文对可能的反应机理进行了简要探讨。