Bimetallic Ruthenium PNP Pincer Complex As a Platform to Model Proposed Intermediates in Dinitrogen Reduction to Ammonia

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.