Hydrogen complexation and activation in metal-free systems

基质分离光谱已被用于研究各种FLPs、金属配合物、碳烯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在3 - 30 K的温度范围内将这些系统在固体氢和h2掺杂的氩气中分离出来。一个缺点是观察到所有被调查的FLPs都具有低挥发性，同时具有热不稳定性。因此，直接升华是不可能的。然而，二氢化的FLP极性更小，挥发性更强，可以升华。在气相中，H2被消除，FLPs现在可以沉积在基质中。这是一个重要的机械结果，因为它证明了H2在气相中的可逆性。根据这一观察，开发了flp6a和类似FLPs的基质分离程序。对FLPs进行了光谱表征，并对其与H2和CO的反应进行了研究。H2和CO都与FLPs形成配合物。一个有趣的系统，即使在低温下也能插入H2，那就是azulenylcarbene 11。这是已知的第二个在低温下插入氢的单线态碳。一个非常强的动力学同位素效应表明量子化学隧穿参与了插入反应。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，我们计划对该系统进行详细的探索。

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.