Molecular and Electronic Structure of Dinuclear Uranium Bis-渭-Oxo Complexes with Diamond Core Structural Motifs

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• 作者：Anna-Corina Schmidt ; Frank W. Heinemann ; Wayne W. Lukens ; Jr. ; Karsten Meyer
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：August 27, 2014
• 年：2014
• 卷：136
• 期：34
• 页码：11980-11993
• 全文大小：663K
• ISSN：1520-5126

文摘

In a multiple-bond metathesis reaction, the triazacyclononane (tacn)-anchored methyl- and neopentyl (nP)-substituted tris(aryloxide) U^III complex [((^nP,MeArO)₃tacn)U^III] (1) reacts with mesityl azide and CO₂ to form mesityl isocyanate and the dinuclear bis(渭-oxo)-bridged U^V/U^V complex [{((^nP,MeArO)₃tacn)U^V}₂(渭-O)₂] (3). This reaction proceeds via the mononuclear U^V imido intermediate [((^nP,MeArO)₃tacn)U^V(NMes)] (2), which has been synthesized and fully characterized independently. The dimeric U^V oxo species shows rich redox behavior: complex 3 can be reduced by one and two electrons, respectively, yielding the mixed-valent U^IV/U^V bis(渭-oxo) complex [K(crypt)][{((^nP,MeArO)₃tacn)U^IV/V}₂(渭-O)₂] (7) and the U^IV/U^IV bis(渭-oxo) complex K₂[{((^nP,MeArO)₃tacn)U^IV}₂(渭-O)₂] (6). In addition, complex 3 can be oxidized to provide the mononuclear uranium(VI) oxo complexes [((^nP,MeArO)₃tacn)U^VI(O)_eq(OTf)_ax] (8) and [((^nP,MeArO)₃tacn)U^VI(O)_eq]SbF₆ (9). The unique series of bis(渭-oxo) complexes also shows notable magnetic behavior, which was investigated in detail by UV/vis/NIR and EPR spectroscopy as well as SQUID magnetization studies. In order to understand possible magnetic exchange phenomena, the mononuclear terminal oxo complexes [((^nP,MeArO)₃tacn)U^V(O)(O-pyridine)] (4) and [((^nP,MeArO)₃tacn)U^V(O)(O-NMe₃)] (5) were synthesized and fully characterized. The magnetic study revealed an unusually strong antiferromagnetic exchange coupling between the two U^V ions in 3. Examination of the ¹⁸O-labeled bis(渭-oxo)-bridged dinuclear complexes 3, 6, and 7 allowed for the first time the unambiguous assignment of the vibrational signature of the [U(渭-O)₂U] diamond core structural motif.