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Hydrogenation and dehydrogenation in potential hydrogen storage compounds

Transition metal hydrides are critically involved in many stoichiometric and catalytic processes in organometallic chemistry, most notably hydrogenation and dehydrogenation reactions. The hydrides display a broad reactivity: hydride donation, protonation, transfer of hydrogen atoms. In the hydrogenation reactions, the crucial step in the reaction path is the co-ordination of an H2 molecule to the metal centre and its activation via the formation of a M(η2-H2) complex, and the subsequent oxidative addition leading to a «M-H» complex.

Moreover the ability of these transition metal complexes of donating or transferring hydrogen atoms or dihydrogen may find an application in the design of new hydrogen-storage materials as, in some specific cases, reversible dihydrogen co-ordination takes place.

For a better understanding of the steric and electronic effects governing these reactions a detailed knowledge of the metal-hydrogen interaction is essential, a knowledge that can only be obtained from accurate structural and dynamical data. Therefore neutron diffraction data are essential.

An important compound of this type is the complex RuH2(H2)2(PCyp3)2, where PCyp3 is tricyclopentylphosphine. D19 work on this (see Figure) has also shown that the compound is not only stable at room temperature but also much more active for H/D exchange and C-C bond coupling than the well-known complex RuH22-H2)2(PCy3)2.

Ref.: Grellier M. , Vendier L. , Chaudret B. , Albinati A. , Rizzato S. , Mason S. , Sabo-Etienne S., J. American Chemical Society 127, 17592-17593 (2005).