Sadique Azwana R, Gregory Elizabeth A, Brennessel William W, Holland Patrick L
Department of Chemistry, University of Rochester, Rochester, NY 14627, USA.
J Am Chem Soc. 2007 Jul 4;129(26):8112-21. doi: 10.1021/ja069199r. Epub 2007 Jun 12.
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 beta-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 eta2-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.
高自旋铁氢化物配合物的反应途径与固氮酶还原N₂的机制相关，据推测该机制涉及顺磁性铁氢化物物种。然而，几乎所有已知的铁氢化物都是低自旋、抗磁性的Fe(II)化合物。我们已经证明，首个高自旋铁氢化物配合物LtBuFeH（LtBu = 庞大的β-二酮亚胺）与PhN=NPh反应会完全切断N-N双键，生成LtBuFeNHPh。在此，我们披露了一系列阐明该反应机制的实验。交叉实验和动力学实验排除了常见的非自由基机制，并支持由包括罕见的η²-偶氮苯配合物在内的铁(I)物种介导的自由基链机制。因此，这种高自旋铁(II)氢化物可以通过非自由基和自由基插入机制断裂N-N键，这一特殊特性赋予了其新颖的反应活性。
