Redox Noninnocence of the Bridge in Copper(II) Salophen and Bis(oxamato) Complexes

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• 作者：David de Bellefeuille ; Maylis Orio ; Anne-Laure Barra ; Ally Aukauloo ; Yves Journaux ; Christian Philouze ; Xavier Ottenwaelder ; Fabrice Thomas
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：September 21, 2015
• 年：2015
• 卷：54
• 期：18
• 页码：9013-9026
• 全文大小：682K
• ISSN：1520-510X

文摘

Two square-planar copper(II) complexes of 1,2-bis(2-hydroxy-3,5-di-tert-butylbenzimino)-4,5-bis(dimethylamino)benzene (1) and N-[4,5-bis(dimethylamino)-2-(oxalylamino)benzene]oxamate (2^2鈥?/b>) were prepared. The crystal structures of the proligands H₂L¹ and Et₂H₂L², as well as the corresponding complexes, are reported. The proligands each display a one-electron-oxidation wave, which is assigned to oxidation of the bis(dimethylamino)benzene moiety into a 蟺 radical. Complexes 1 and 2^2鈥?/b> exhibit reversible one-electron-oxidation waves in their cyclic voltammograms (E_1/2¹ = 0.14 and E_1/2² = 0.31 V for 1 and E_1/2¹ = 鈭?.47 V vs Fc⁺/Fc for 2^2鈥?/b>). The first process corresponds to oxidation of the bis(dimethylamino)benzene central ring into a 蟺 radical, while the second process for 1 is ascribed to oxidation of the 蟺 radical into an 伪-diiminoquinone. The one-electron-oxidized species 1⁺ and 2^鈥?/b> exhibit intense visible鈥搉ear-IR absorptions, which are diagnostic of 蟺 radicals. They display a triplet signal in their electron paramagnetic resonance spectra, which stem from magnetic coupling between the ligand-radical spin and the copper(II) spin. The zero-field-splitting parameters are larger for 2^鈥?/b> than 1⁺ because of greater delocalization of the spin density onto the coordinated amidato N atoms. Density functional theory calculations support a 蟺-radical nature of the one-electron-oxidized complexes, as well as S = 1 ground spin states. The electrogenerated 1²⁺ comprises a closed-shell diiminoquinone ligand coordinated to a copper(II) metal center. Both 1 and 2 catalyze the aerobic oxidation of benzyl alcohol, albeit with different yields.