In this work, we report the room-temperature N–H bond activation of ammonia by the carboranyl diphosphine 1-P^tBu₂-2-PⁱPr₂-closo-C₂B₁₀H₁₀ (1) resulting in the formation of zwitterionic 7-P(NH₂)^tBu₂-10-P(H)ⁱPr₂-nido-C₂B₁₀H₁₀ (2). Unlike the other phosphorus-based ambiphiles that require geometric constraints to enhance electrophilicity, the new mode of bond activation in this main-group system is based on the cooperation between electron-rich trigonal phosphine centers and the electron-accepting carborane cluster. As an exception among many other metal-based and metal-free systems, the N–H bond activation of gaseous ammonia or aqueous ammonium hydroxide by carboranyl diphosphine 1 proceeds with tolerance of air and water. Mechanistic details of ammonia activation were explored computationally by DFT methods, demonstrating an electrophilic activation of ammonia by the phosphine center. This process is driven by the reduction of the boron cluster followed by an ammonia-assisted deprotonation and proton transfer. A subsequent reaction of 2 and TEMPO results in the cleavage of all N–H and P–H bonds with the formation of a cyclic phosphazenium cation supported by an anionic cluster N(7-P^tBu₂-8-PⁱPr₂)-nido-C₂B₉H₁₀ (3). Transformations reported herein represent the first example of ammonia oxidation via triple hydrogen atom abstraction facilitated by a metal-free system.

中文翻译：

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氧化还原活性碳硼烷基二膦对氨的 N-H 键活化


在这项工作中，我们报道了碳硼酰二膦 1-P^tBu 2-2-PPr 2-closo-C 2 B₁₀H₁₀ （1） 在室温下激活氨，导致形成两性离子 7-P（NH₂）^tBu_2-10-P（H）Pr 2-nido-C₂B₁₀H₁₀ （2).与其他需要几何约束来增强亲电性的磷基双亲物不同，该主族系统中的新键激活模式基于富电子三角膦中心和接受电子的碳硼烷簇之间的合作。与许多其他金属基和无金属体系不同，碳硼酰二膦 1 对气态氨或氢氧化铵水溶液的 N-H 键活化在耐空气和水的情况下进行。通过 DFT 方法对氨活化的机理细节进行了计算探索，证明了磷化氢中心对氨的亲电活化。这个过程是由硼簇的还原驱动的，然后是氨辅助的去质子化和质子转移。随后的 2 和 TEMPO 反应导致所有 N-H 和 P-H 键裂解，形成由阴离子簇 N（7-P^tBu 2-8-PPr₂）-nido-C ₂B₉H₁₀ 支持的环状磷化阳离子 （3）。本文报道的转化代表了无金属系统促进的通过三氢原子提取进行氨氧化的第一个例子。