Road maps for nitrogen-transfer catalysis: the challenge of the osmium(VIII)-catalyzed diamination

Although the Sharpless dihydroxylation has been used on laboratory and industrial scales for several decades, an analogous osmium-catalyzed diamination is unknown. To explore the reaction of osmium(VIII) oxo-imido complexes with C=C bonds, density functional calculations have been performed. The calculations predict a chemoselective and perispecific [3+2] addition of the NH=Os=NH moiety of diimidodioxoosmium(VIII) to ethylene, yielding dioxoosma-2,5-diazolidine. At first sight, this metallacycle seems extremely stable; it is more stable than diimidoosma-2,5-dioxolane by 40 kcal mol(-1). However, a comparison of the thermodynamic reaction profiles for catalytic model cycles of dihydroxylation, aminohydroxylation, and diamination reveals that, contrary to common belief, the instability of the metal=N bond in the osmium(VIII) imido complex rather than the stability of the metal-N bond in the osmium(VI) intermediate causes most of the energy difference between the metallacycles. Substituents on the substrate have a small effect on the thermodynamic reaction profiles, whereas substituents on the imido ligands allow steric and electronic control of the reaction free enthalpies in the range of up to 25 kcal mol(-1). The results of this study help identify potential challenges in the development of the as-yet hypothetical title reaction and provide a modular concept for exploring novel catalytic routes.