A Terminal Osmium(IV) Nitride: Ammonia Formation and Ambiphilic Reactivity

Low-valent osmium nitrides are discussed as intermediates in nitrogen fixation schemes. However, rational synthetic routes that lead to isolable examples are currently unknown. Here, the synthesis of the square-planar osmium(IV) nitride [OsN(PNP)] (PNP=N(CH2CH2P(tBu)(2))(2)) is reported upon reversible deprotonation of osmium(VI) hydride [Os(N)H(PNP)](+). The Os-IV complex shows ambiphilic nitride reactivity with SiMe3Br and PMe3, respectively. Importantly, the hydrogenolysis with H-2 gives ammonia and the polyhydride complex [OsH4(HPNP)] in 80% yield. Hence, our results directly demonstrate the role of low-valent osmium nitrides and of heterolytic H-2 activation for ammonia synthesis with H-2 under basic conditions.