具十五族配位基之硼陽離子

Abstract

為了要達成更高的路易士酸性，我們利用碳烯及吡啶組成的雙牙配基來穩定硼陽離子，並且由核磁共振與單晶鑑定；可惜，後續拔除氯離子的反應並不順利，無法如預期得到雙牙配基所穩定的兩價硼陽離子。另外，我們意外的發現吡啶碳烯與硼陽離子會進行氧化還原反應；根據理論計算，硼陽離子被碳烯還原後，會脫去一個氯離子，形成一個帶正電的自由基。此外，本研究也發現由低價數磷所組成的配基，並不適合用來配位硼化合物；Phospha-Wittig中的磷-磷鍵以及碳烯穩定的磷烯中的磷-碳鍵，在遇到硼烷後都會斷裂，至於二磷烯則因為立體障礙過大，而無法在磷上接上硼烷。

To achieve higher Lewis acidity of the boron species, a bidentate pyridyl-carbene stabilized boron cation is synthesized and characterized by NMR and X-ray crystallography. Unfortunately, the following chloride abstraction did not resulted in the targeted dicationic compound. Interestingly, an unexpected redox reaction of the boron cation and carbene was discovered during the synthesis of boronium. As indicated by theoretical calculations, the boronium would be reduced by carbene to yield a neutral radical, which then dissociates a chloride anion to form a radical cation. On the other hand, this study also revealed that the low-valent phosphorous-based ligands are proven to be not suitable towards Lewis acidic boranes. The P-P bond in phospha-Wittig and the P-C bond in NHC-stabilized phosphinidene readily break when treated with boranes, whereas diphosphene remained unreacted due to steric congestion at phosphorous center.