Formation Mechanisms, Structure, Solution Behavior, and Reactivity of Aminodiborane

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• 作者：Huizhen Li ; Nana Ma ; Wenjuan Meng ; Judith Gallucci ; Yongqing Qiu ; Shujun Li ; Qianyi Zhao ; Jie Zhang ; Ji-Cheng Zhao ; Xuenian Chen
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：September 30, 2015
• 年：2015
• 卷：137
• 期：38
• 页码：12406-12414
• 全文大小：519K
• ISSN：1520-5126

文摘

A facile synthesis of cyclic aminodiborane (NH₂B₂H₅, ADB) from ammonia borane (NH₃路BH₃, AB) and THF路BH₃ has made it possible to determine its important characteristics. Ammonia diborane (NH₃BH₂(渭-H)BH₃, AaDB) and aminoborane (NH₂BH₂, AoB) were identified as key intermediates in the formation of ADB. Elimination of molecular hydrogen occurred from an ion pair, [H₂B(NH₃) (THF)]⁺[BH₄]^{鈭?/sup>. Protic-hydridic hydrogen scrambling was proved on the basis of analysis of the molecular hydrogen products, ADB and other reagents through 2H NMR and MS, and it was proposed that the scrambling occurred as the ion pair reversibly formed a BH₅-like intermediate, [(THF)BH₂NH₂](畏2-H₂)BH₃. Loss of molecular hydrogen from the ion pair led to the formation of AoB, most of which was trapped by BH₃ to form ADB with a small amount oligomerizing to (NH₂BH₂)_n. Theoretical calculations showed the thermodynamic feasibility of the proposed intermediates and the activation processes. The structure of the ADB路THF complex was found from X-ray single crystal analysis to be a three-dimensional array of zigzag chains of ADB and THF, maintained by hydrogen and dihydrogen bonding. Room temperature exchange of terminal and bridge hydrogens in ADB was observed in THF solution, while such exchange was not observed in diethyl ether or toluene. Both experimental and theoretical results confirm that the B鈥揌鈥揃 bridge in ADB is stronger than that in diborane (B₂H₆, DB). The B鈥揌鈥揃 bridge is opened when ADB and NaH react to form sodium aminodiboronate, Na[NH₂(BH₃)₂]. The structure of the sodium salt as its 18-crown-6 ether adduct was determined by X-ray single crystal analysis.}