Hydrogen complexation and activation in metal-free systems

基质分离光谱已用于研究各种FLP、金属配合物、卡宾和模型化合物与分子氢的相互作用和反应。我们的实验装置使我们能够隔离这些系统在固体氢以及H2掺杂的氩气在温度范围从3 - 30 K。一个缺点是观察到所有研究的FLP都具有低挥发性，同时热不稳定。因此，直接升华是不可能的。然而，二氢化的FLP极性较小，挥发性更强，并且可以升华。在气相中，H2被消除，并且FLP现在可以沉积在基质中。这是一个重要的机理结果，因为它证明了在气相中H2加成的可逆性。从这一观察，开发了一种用于FLP 6a和类似FLP的基质分离的程序。的FLP进行了光谱表征，并与H2和CO的反应进行了研究。H2和CO都能与FLP形成络合物，一个有趣的体系是奥基卡宾11，它甚至在低温下也能插入H2。这是已知的第二个在低温下插入氢中的单线态卡宾。一个非常强的动力学同位素效应表明，量子化学隧穿参与插入反应。由于隧穿是一种非常基本的现象，可能在许多涉及H2的反应中发挥作用，因此我们计划详细探索这个系统。

Matrix isolation spectroscopy has been used to investigate the interactions and reactions of a variety of FLPs, metal complexes, carbenes, and model compounds with molecular hydrogen. Our experimental set-up allows us to isolate these systems in solid hydrogen as well as H2-doped argon at temperatures ranging from 3 – 30 K. A draw-back was the observation that all FLPs investigated are of low volatility and at the same time thermally labile. Thus, a direct sublimation was not possible. However, the dihydrogenated FLP are less polar and more volatile and can be sublimed. In the gas phase H2 is eliminated and the FLPs can now be deposited in matrices. This is a mechanistic important result since it demonstrates the reversibility of the H2 addition in the gas phase.From that observation, a procedure was developed for the matrix-isolation of FLP 6a and similar FLPs. The FLPs were spectroscopically characterized and reactions with H2 and CO investigated. Both H2 and CO form complexes with the FLPs.An interesting system that inserts into H2 even at cryogenic temperatures is azulenylcarbene 11. This is only the second singlet carbene known to insert into hydrogen at cryogenic temperatures. A very strong kinetic isotope effect suggests that quantum chemical tunneling is involved in the insertion reaction. Since tunneling is a very basic phenomenon that might play a role in many reactions involving H2, we plan to explore this system in great detail.