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Mechanistic Insight into NN Cleavage by a Low-Coordinate Iron(II) Hydride Complex

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posted on 2007-07-04, 00:00 authored by Azwana R. Sadique, Elizabeth A. Gregory, William W. Brennessel, Patrick L. Holland
The reaction pathways of high-spin iron hydride complexes are relevant to the mechanism of N2 reduction by nitrogenase, which has been postulated to involve paramagnetic iron-hydride species. However, almost all known iron hydrides are low-spin, diamagnetic Fe(II) compounds. We have demonstrated that the first high-spin iron hydride complex, LtBuFeH (LtBu = bulky β-diketiminate), reacts with PhNNPh to completely cleave the N−N double bond, giving LtBuFeNHPh. Here, we disclose a series of experiments that elucidate the mechanism of this reaction. Crossover and kinetic experiments rule out common nonradical mechanisms, and support a radical chain mechanism mediated by iron(I) species including a rare η2-azobenzene complex. Therefore, this high-spin iron(II) hydride can break N−N bonds through both nonradical and radical insertion mechanisms, a special feature that enables novel reactivity.