CH Activation of Cationic Bismuth Amides: Heteroaromaticity, Derivatization, and Lewis Acidity

Cationization of
Bi­(NPh2)3 has recently been
reported to allow access to single- and double-CH activation reactions,
followed by selective transformation of Bi–C into C–X
functional groups (X = electrophile). Here we show that this approach
can successfully be transferred to a range of bismuth amides with
two aryl groups at the nitrogen, Bi­(NRaryl2)3. Exchange of one nitrogen-bound aryl group for an alkyl substituent
gave the first example of a homoleptic bismuth amide with a mixed
aryl/alkyl substitution pattern at the nitrogen, Bi­(NPhiPr)3. This compound is susceptible to selective N–N
radical coupling in its neutral form and also undergoes selective
CH activation when transformed into a cationic species. The second
CH activation is blocked due to the absence of a second aryl moiety
at nitrogen. The Lewis acidity of neutral bismuth amides is compared
with that of cationic species “[Bi­(aryl)­(amide)­(L)n]+” and “[Bi­(aryl)2(L)n]+” based on the
(modified) Gutmann–Beckett method (L = tetrahydrofuran or pyridine).
The heteroaromatic character of [Bi­(C6H3R)2NH­(triflate)] compounds, which are iso-valence-electronic
with anthracene, is investigated by theoretical methods. Analytical
methods used in this work include nuclear magnetic resonance spectroscopy,
single-crystal X-ray diffraction, mass spectrometry, and density functional
theory calculations.

近期有研究报道，对三(二苯基氨基)铋（Bi(NPh₂)₃）进行阳离子化处理，可实现单碳氢键与双碳氢键活化反应，随后可将铋-碳（Bi–C）键选择性转化为碳-亲电试剂（C–X，X为亲电试剂）官能团。
本研究表明，该策略可成功拓展至一系列氮原子上连有两个芳基的铋酰胺类化合物Bi(NRᵃʳʸˡ₂)₃。将氮原子结合的一个芳基替换为烷基取代基，得到了首例在氮原子上具有混合芳基/烷基取代模式的均配型铋酰胺——三(N-苯基-N-异丙基氨基)铋（Bi(NPhᵢPr)₃）。
该化合物在中性状态下可发生选择性氮-氮（N–N）自由基偶联反应，转化为阳离子物种后则可发生选择性碳氢键活化；由于氮原子上缺少第二个芳基取代基，第二次碳氢键活化反应被阻断。
本研究基于改进型古特曼-贝克特法（Gutmann–Beckett method），对比了中性铋酰胺与阳离子物种"[Bi(芳基)(酰胺)(L)ₙ]⁺"和"[Bi(芳基)₂(L)ₙ]⁺"（L为四氢呋喃或吡啶）的路易斯酸性。
本研究通过理论方法，对与蒽为价电子等价体的[Bi(C₆H₃R)₂NH(三氟甲磺酸盐)]类化合物的杂芳环特性进行了探究。
本研究采用的分析表征手段包括核磁共振波谱法（NMR）、单晶X射线衍射、质谱分析法以及密度泛函理论（DFT）计算。