Three-Coordinate Terminal Imidoiron(III) Complexes: Structure, Spectroscopy, and Mechanism of Formation

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• 作者：Ryan E. Cowley ; Nathan J. DeYonker ; Nathan A. Eckert ; Thomas R. Cundari ; Serena DeBeer ; Eckhard Bill ; Xavier Ottenwaelder ; Christine Flaschenriem ; Patrick L. Holland
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：July 5, 2010
• 年：2010
• 卷：49
• 期：13
• 页码：6172-6187
• 全文大小：1201K
• 年卷期：v.49,no.13(July 5, 2010)
• ISSN：1520-510X

文摘

Reaction of 1-adamantyl azide with iron(I) diketiminate precursors gives metastable but isolable imidoiron(III) complexes LFe═NAd (L = bulky β-diketiminate ligand; Ad = 1-adamantyl). This paper addresses (1) the spectroscopic and structural characterization of the Fe═N multiple bond in these interesting three-coordinate iron imido complexes, and (2) the mechanism through which the imido complexes form. The iron(III) imido complexes have been examined by ¹H NMR and electron paramagnetic resonance (EPR) spectroscopies and temperature-dependent magnetic susceptibility (SQUID), and structurally characterized by crystallography and/or extended X-ray absorption fine structure (EXAFS) measurements. These data show that the imido complexes have quartet ground states and short (1.68 ± 0.01 Å) iron−nitrogen bonds. The formation of the imido complexes proceeds through unobserved iron−N₃R intermediates, which are indicated by QM/MM computations to be best described as iron(II) with an N₃R radical anion. The radical character on the organoazide bends its NNN linkage to enable easy N₂ loss and imido complex formation. The product distribution between imidoiron(III) products and hexazene-bridged diiron(II) products is solvent-dependent, and the solvent dependence can be explained by coordination of certain solvents to the iron(I) precursor prior to interaction with the organoazide.