Bimetallic Ruthenium PNP
Pincer Complex As a Platform to Model Proposed Intermediates in Dinitrogen
Reduction to Ammonia
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Abstract
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(N<sub>2</sub>)]<sub>2</sub>(μ-Cl)<sub>2</sub>}(BF<sub>4</sub>)<sub>2</sub> (<b>2</b>) (HPNP = HN(CH<sub>2</sub>CH<sub>2</sub>P<sup>i</sup>Pr<sub>2</sub>)<sub>2</sub>) reacted with 1 equiv of hydrazine
to generate [(HPNPRu)<sub>2</sub>(μ<sup>2</sup>-H<sub>2</sub>NNH<sub>2</sub>)(μ-Cl)<sub>2</sub>](BF<sub>4</sub>)<sub>2</sub> (<b>3</b>) and with an excess of the reagent to form [HPNPRu(NH<sub>3</sub>)(κ<sup>2</sup>-N<sub>2</sub>H<sub>4</sub>)](BF<sub>4</sub>)Cl (<b>5</b>). When phenylhydrazine was added to <b>2</b>, the diazene species [(HPNPRu)<sub>2</sub>(μ<sup>2</sup>-HNNPh)(μ-Cl)<sub>2</sub>](BF<sub>4</sub>)<sub>2</sub> (<b>4</b>) was obtained. Treatment of <b>2</b> with H<sub>2</sub> or CO yielded {[HPNPRu(H<sub>2</sub>)]<sub>2</sub>(μ-Cl)<sub>2</sub>}(BF<sub>4</sub>)<sub>2</sub> (<b>7</b>) and [HPNPRuCl(CO)<sub>2</sub>]BF<sub>4</sub> (<b>8</b>), respectively. Abstraction
of chloride using AgOSO<sub>2</sub>CF<sub>3</sub> or AgBPh<sub>4</sub> afforded the species [(HPNPRu)<sub>2</sub>(μ<sup>2</sup>-OSO<sub>2</sub>CF<sub>3</sub>)(μ-Cl)<sub>2</sub>]OSO<sub>2</sub>CF<sub>3</sub> (<b>9</b>) and [(HPNPRu)<sub>2</sub>(μ-Cl)<sub>3</sub>]BPh<sub>4</sub> (<b>10</b>), respectively. Complex <b>3</b> reacted with HCl/H<sub>2</sub>O or HCl/Et<sub>2</sub>O to
produce ammonia stoichiometrically; the complex catalytically disproportionates
hydrazine to generate ammonia
