Ruthenium-Catalyzed Dehydrogenation of Ammonia Boranes

Ammonia borane (AB), which has a very high hydrogen content by weight (19.6%), is attracting attention as a means of achieving efficient chemical hydrogen storage.1,2 Heating AB in the solid state,3 ionic liquids4 or the presence of acid5 has been shown to induce the release of>1.0 equiv of H2 over the course of several hours, and transition metal complexes of Rh,6 Ni,7 and Ir8 have been shown to catalyze H2 release under mild conditions. Notably, the Ni catalysts described by Baker release up to 2.8 equiv of H2,7 an observation that has prompted a more detailed evaluation of their reaction mechanism.9a When considering strategies for de-hydrogenation, AB is often compared to ethane.10 Computational predictions provide little mechanistic support for this analogy, however,9,11 and in terms of local dipoles and reactivity AB may better be compared to methanol. Drawing from this analogy, we have discovered that ruthenium catalysts, originally developed fo