Anion Effects in Oxidative Aliphatic Carbon–Carbon Bond Cleavage Reactions of Cu(II) Chlorodiketonate Complexes

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• 作者：Sushma L. Saraf ; Anna Miłaczewska ; Tomasz Borowski ; Christopher D. James ; David L. Tierney ; Marina Popova ; Atta M. Arif ; Lisa M. Berreau
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：July 18, 2016
• 年：2016
• 卷：55
• 期：14
• 页码：6916-6928
• 全文大小：687K
• 年卷期：0
• ISSN：1520-510X

文摘

Aliphatic oxidative carbon–carbon bond cleavage reactions involving Cu(II) catalysts and Ob>2b> as the terminal oxidant are of significant current interest. However, little is currently known regarding how the nature of the Cu(II) catalyst, including the anions present, influence the reaction with Ob>2b>. In previous work, we found that exposure of the Cu(II) chlorodiketonate complex [(6-Phb>2b>TPA)Cu(PhC(O)CClC(O)Ph)]ClOb>4b> (<b>1b>) to Ob>2b> results in oxidative aliphatic carbon–carbon bond cleavage within the diketonate unit, leading to the formation of benzoic acid, benzoic anhydride, benzil, and 1,3-diphenylpropanedione as organic products. Kinetic studies of this reaction revealed a slow induction phase followed by a rapid decay of the absorption features of <b>1b>. Notably, the induction phase is not present when the reaction is performed in the presence of a catalytic amount of chloride anion. In the studies presented herein, a combination of spectroscopic (UV–vis, EPR) and density functional theory (DFT) methods have been used to examine the chloride and benzoate ion binding properties of <b>1b> under anaerobic conditions. These studies provide evidence that each anion coordinates in an axial position of the Cu(II) center. DFT studies reveal that the presence of the anion in the Cu(II) coordination sphere decreases the barrier for Ob>2b> activation and the formation of a Cu(II)–peroxo species. Notably, the chloride anion more effectively lowers the barrier associated with O–O bond cleavage. Thus, the nature of the anion plays an important role in determining the rate of reaction of the diketonate complex with Ob>2b>. The same type of anion effects were observed in the Ob>2b> reactivity of the simple Cu(II)–bipyridine complex [(bpy)Cu(PhC(O)C(Cl)C(O)Ph)ClOb>4b>] (<b>3b>).