Rare Earth Metal Complexes of Bidentate Nitroxide Ligands: Synthesis and Electrochemistry

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• 作者：Jee Eon Kim ; Justin A. Bogart ; Patrick J. Carroll ; Eric J. Schelter
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：January 19, 2016
• 年：2016
• 卷：55
• 期：2
• 页码：775-784
• 全文大小：606K
• ISSN：1520-510X

文摘

We report rare earth metal complexes with tri- and bidentate ligands including strongly electron-donating nitroxide groups. The tridentate ligand 1,3,5-tris(2′-tert-butylhydroxylaminoaryl)benzene (H₃arene-triNOx) was complexed to cerium(IV) in a 2:1 ligand-to-metal stoichiometry as Ce(Harene-triNOx)₂ (1). Cyclic voltammetry of this compound showed stabilization of the tetravalent cerium cation with a Ce(IV/III) couple at E_1/2 = ?1.82 V versus Fc/Fc⁺. On the basis of the uninvolvement of the third nitroxide group in the coordination chemistry with the cerium(IV) cation, the ligand system was redesigned toward a simpler bidentate mode, and a series of rare earth metal–arene-diNOx complexes were prepared with La(III), Ce(IV), Pr(III), Tb(III), and Y(III), [RE(arene-diNOx)₂]^? ([2–RE]^?, RE = La, Pr, Y, Tb) and Ce^IV(arene-diNOx)₂, where H₂arene-diNOx = 1,3-bis(2′-tert-butylhydroxylaminoaryl)benzene. The core structures were isostructural throughout the series, with three nitroxide groups in η² binding modes and one κ¹ nitroxide group coordinated to the metal center in the solid state. In all cases except Ce^IV(arene-diNOx)₂, electrochemical analysis described two subsequent, ligand-based, quasi-reversible redox waves, indicating that a stable [N–O?] group was generated on the electrochemical time scale. Chemical oxidation of the terbium complex was performed, and isolation of the resulting complex, Tb(arene-diNOx)₂·CH₂Cl₂ (3·CH₂Cl₂), confirmed the assignment of the cyclic voltammograms. Magnetic data showed no evidence of mixing between the Tb(III) states and the states of the open-shell ligand.