Department of Materials Science, Fudan University, No. 220 Handan Road, Shanghai, 200433, P.R. China.
Inorg Chem. 2011 May 16;50(10):4301-6. doi: 10.1021/ic200373g. Epub 2011 Apr 14.
This paper reports for the first time that under ammonia atmosphere, ammonia borane (AB) reversibly absorbs up to at least 6 equiv of NH(3), forming liquid AB(NH(3))(n) (n = 1-6) complexes at 0 °C. Reasonable structures for AB(NH(3))(n) were identified via density functional theory calculations, which indicate that the strong classical hydrogen bond formed between the lone pair of NH(3) and the -NH(3) of AB is the driving force for the absorption of ammonia by AB. By use of the van't Hoff equation, the enthalpy change (ΔH) for AB to absorb one NH(3) was determined to be -2.24 kcal/mol, which is in good agreement with the theoretical calculations. Other organic amines were screened to further confirm the role of the N lone pair; only 1,4-diazabicyclo[2.2.2]octane (DABCO) formed a stable adduct, which X-ray structural analysis showed was the DABCO-BH(3) species. Finally, Raman spectra of AB(NH(3))(n) were collected, and its unique spectral features are also discussed.
本文首次报道，在氨气氛下，氨硼烷（AB）在 0°C 下可可逆地吸收多达至少 6 当量的 NH3，形成液态 AB(NH3)n（n=1-6）配合物。通过密度泛函理论计算确定了 AB(NH3)n的合理结构，表明 AB 与 NH3的孤对之间形成的强经典氢键是 AB 吸收氨的驱动力。根据范特霍夫方程，确定 AB 吸收一个 NH3的焓变（ΔH）为-2.24 kcal/mol，这与理论计算非常吻合。还筛选了其他有机胺以进一步确认 N 孤对的作用；只有 1,4-二氮杂二环[2.2.2]辛烷（DABCO）形成了稳定的加合物，X 射线结构分析表明其为 DABCO-BH3物种。最后，收集了 AB(NH3)n的拉曼光谱，并对其独特的光谱特征进行了讨论。
