Hydrogen complexation and activation in metal-free systems

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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.