Two 2-[bis(pentafluorophenyl)boryl]-N,N-dialkylanilines reported here exemplify a new class of intramolecular frustrated B/N Lewis pairs. A structure closely related to this class structure was synthesized in 2003 by Piers et al. but was unable to activate H2. The new aminoboranes can activate hydrogen at near ambient conditions; besides, one of them can hydrogenate imines and enamines in a catalytic fashion demonstrating the validity of the original Piersâ approach to hydrogen activation with ansa-aminoboranes.
N-TMPN-CH2C6H4B(C6F5)2 (where TMPNH is 2,2,6,6-tetramethylpiperidinyl) which is able to reversibly activate H2 through an intramolecular mechanism is synthesized. This new substance makes use of the concept of moleculartweezers where the active N and B centers are located close to each other so that one H2 molecule can fit in this void and be activated. Because of the fixed geometry of this ansa-ammonium-borate it forms
合成了第一个能够通过分子内机制可逆地激活 H2 的 ansa-aminoborane N-TMPN-CH2C6H4B(C6F5)2(其中 TMPNH 是 2,2,6,6-四甲基哌啶基)。这种新物质利用分子镊子的概念,其中活性 N 和 B 中心彼此靠近,因此一个 H2 分子可以放入这个空隙中并被激活。由于这种柄型硼酸铵的固定几何形状,它形成了一个 1.78 A 的短 NH...HB 二氢键,由 X 射线分析确定。因此,结合氢可以在 100 摄氏度以上释放。 此外,短 H...H 接触和 NH...H(154 度)和 BH...H(125 度)角表明二氢N-TMPNH-CH2C6H4BH(C6F5)2 中的相互作用本质上是部分共价的。作为讨论机制的基础,进行了量子化学计算,发现分裂 H2 所需的能量可以来自所得离子碎片之间的库仑吸引力,或“库仑为 Heitler-London 买单”。空气和水分稳定的
Molecular Hydrogen Tweezers: Structure and Mechanisms by Neutron Diffraction, NMR, and Deuterium Labeling Studies in Solid and Solution
variable-temperature NMR spectroscopy. We synthesized stable, individual isotopic isomers NDDB, NHDB, and NDHB. NMR measurements revealed a primary isotope effect in the chemical shift difference (p)Δ(1)H(D) = δ(NH) - δ(ND) (0.56 ppm), and hence supported dihydrogen bonding. The NMR studies gave strong evidence that the structure of NHHB in solution is similar to that in the solidstate. This is corroborated