Thermal Dehydrogenation of Dimethylamine Borane Catalyzed by a Bifunctional Rhenium Complex

The reaction of a bidentate pyrrole based rhenium tetracarbonyl complex with dimethylamine borane at room temperature results in rapid dehydrogenation. Hydrogen generation was detected at temperatures as low as 238 K, and NMR spectroscopy provided evidence for the initial formation of a Re-H-B sigma bound adduct at these temperatures. The rate of the dehydrocoupling reaction was significantly influenced by the electron density on the metal center and the identity of the alkyl group (CH3 or CF3) on the ketone carbon of the pyrrole ligand. The bifunctional nature of this complex incorporating both an acidic Re center and a basic oxygen center, coupled with the hemilability of the organic carbonyl group, are key motifs of this catalyst that result in the thermal dehydrogenation of dimethylamine borane.