Bimetallic Ruthenium PNP Pincer Complex As a Platform to Model Proposed Intermediates in Dinitrogen Reduction to Ammonia
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A series of ruthenium complexes was isolated and characterized in the course of reactions aimed at studying the reduction of hydrazine to ammonia in bimetallic systems. The diruthenium complex {[HPNPRu(N2)]2(μ-Cl)2}(BF4)2 (2) (HPNP = HN(CH2CH2PiPr2)2) reacted with 1 equiv of hydrazine to generate [(HPNPRu)2(μ2-H2NNH2)(μ-Cl)2](BF4)2 (3) and with an excess of the reagent to form [HPNPRu(NH3)(κ2-N2H4)](BF4)Cl (5). When phenylhydrazine was added to 2, the diazene species [(HPNPRu)2(μ2-HNNPh)(μ-Cl)2](BF4)2 (4) was obtained. Treatment of 2 with H2 or CO yielded {[HPNPRu(H2)]2(μ-Cl)2}(BF4)2 (7) and [HPNPRuCl(CO)2]BF4 (8), respectively. Abstraction of chloride using AgOSO2CF3 or AgBPh4 afforded the species [(HPNPRu)2(μ2-OSO2CF3)(μ-Cl)2]OSO2CF3 (9) and [(HPNPRu)2(μ-Cl)3]BPh4 (10), respectively. Complex 3 reacted with HCl/H2O or HCl/Et2O to produce ammonia stoichiometrically; the complex catalytically disproportionates hydrazine to generate ammonia.
