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

摘要

The reaction pathways of high-spin iron hydride complexes are relevant to the mechanism of N_2 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, L~(tBu)FeH (L~(tBu) = bulky β-diketiminate), reacts with PhN = NPh to completely cleave the N-N double bond, giving L~(tBu)FeNHPh. 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 η~2-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.