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Catalytic Nitrogen-to-Ammonia Conversion by Osmium and Ruthenium Complexes
- Fajardo, Javier, Peters, Jonas C.
- Journal of the American Chemical Society 2017 v.139 no.45 pp. 16105-16108
- ammonia, catalytic activity, hydrides, iron, nitrogen, osmium, reducing agents, ruthenium
- Despite the critical role Ru and Os complexes have played in the development of transition metal dinitrogen chemistry, they have not been shown to mediate catalytic N₂-to-NH₃ conversion (N₂RR), nor have M-NₓHy complexes been derived from protonation of their M-N₂ precursors. To help delineate factors for N₂RR catalysis, we report on isostructural tris(phosphino)silyl Ru and Os complexes that mediate catalytic N₂RR, and compare their activities with an isostructural Fe complex. The Os system is most active, and liberates more than 120 equiv NH₃ per Os center in a single batch experiment using Cp*₂Co and [H₂NPh₂][OTf] as reductant and acid source. Isostructural Ru and Fe complexes generate little NH₃ under the same conditions. Protonation of Os-N₂– affords a structurally characterized Os=NNH₂⁺ hydrazido species that mediates NH₃ generation, suggesting it is a plausible intermediate of the catalysis. Inactive Os hydrides are characterized that form during catalysis.