Humphries Amanda L, Tellier Gabrielle A, Smith Mark D, Chianese Anthony R, Peryshkov Dmitry V
Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter St., Columbia, South Carolina 29208, United States.
Department of Chemistry, Colgate University, 13 Oak Drive, Hamilton, New York 13346, United States.
J Am Chem Soc. 2024 Dec 4;146(48):33159-33168. doi: 10.1021/jacs.4c12146. Epub 2024 Nov 19.
In this work, we report the room-temperature N-H bond activation of ammonia by the carboranyl diphosphine 1-PBu-2-PPr--CBH () resulting in the formation of zwitterionic 7-P(NH)Bu-10-P(H)Pr--CBH (). 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 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 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-PBu-8-PPr)--CBH (). Transformations reported herein represent the first example of ammonia oxidation via triple hydrogen atom abstraction facilitated by a metal-free system.
在本工作中，我们报道了碳硼烷二膦1-PBu-2-PPr--CBH（）在室温下对氨的N-H键活化作用，从而形成两性离子7-P(NH)Bu-10-P(H)Pr--CBH（）。与其他需要几何限制来增强亲电性的磷基两可亲试剂不同，这个主族体系中的新键活化模式是基于富电子的三角膦中心与吸电子的碳硼烷簇之间的协同作用。作为许多其他金属基和无金属体系中的一个例外，碳硼烷二膦对气态氨或氢氧化铵水溶液的N-H键活化在空气和水存在的情况下仍能进行。通过密度泛函理论（DFT）方法对氨活化的机理细节进行了计算研究，结果表明氨是通过膦中心进行亲电活化的。这个过程是由硼簇的还原作用驱动的，随后是氨辅助的去质子化和质子转移。和2,2,6,6-四甲基哌啶氧化物（TEMPO）的后续反应导致所有N-H和P-H键的断裂，形成一个由阴离子簇N(7-PBu-8-PPr)--CBH（）支撑的环状磷氮阳离子。本文报道的转化反应代表了无金属体系促进的通过三次氢原子提取实现氨氧化的首个实例。
