Department of Chemistry, College of Science, Rikkyo University, Toshima, Tokyo, Japan.
Dalton Trans. 2011 Mar 14;40(10):2225-33. doi: 10.1039/c0dt00977f. Epub 2010 Dec 23.
The bridging ligand, 1,8-bis(2,2':6',2''-terpyrid-4'-yl)anthracene (btpyan) was synthesized by the Miyaura-Suzuki cross coupling reaction of anthracenyl-1,8-diboronic acid and 4'-triflyl-2,2':6'-2''-terpyridine in the presence of Pd(PPh(3))(4) (5 mol%) with 68% in yield. Three ruthenium-dioxolene dimers, Ru(2)(OH)(2)(dioxolene)(2)(btpyan) (dioxolene = 3,6-di-tert-butyl-1,2-benzosemiquinone (1), 3,5-dichloro-1,2-benzosemiquinone (2) and 4-nitro-1,2-benzosemiquinone (3)) were prepared by the reaction of Ru(2)Cl(6)(btpyan) with the corresponding catechol. The electronic structure of 1 is approximated by Ru(II)(2)(OH)(2)(sq)(2)(btpyan) (sq = semiquinonato). On the other hand, the electronic states of 2 and 3 are close to Ru(III)(2)(OH)(2) (cat)(2)(btpyan) (cat = catecholato), indicating that a dioxolene having electron-withdrawing groups stabilizes Ru(III)(2)(OH)(2)(cat)(2)(btpyan) rather than Ru(II)(2)(OH)(2)(sq)(2)(btpyan) as resonance isomers. No sign was found of deprotonation of the hydroxo groups of 1, whereas 2 and 3 showed an acid-base equilibrium in treatments with t-BuOLi followed by HClO(4). Furthermore, controlled potential electrolysis of 1 deposited on an ITO (indium-tin oxide) electrode catalyzed the four-electron oxidation of H(2)O to evolve O(2) at potentials more positive than +1.6 V (vs. SCE) at pH 4.0. On the other hand, the electrolysis of 2 and 3 deposited on ITO electrodes did not show catalytic activity for water oxidation under similar conditions. Such a difference in the reactivity among 1, 2 and 3 is ascribed to the shift of the resonance equilibrium between Ru(II)(2)(OH)(2)(sq)(2)(btpyan) and Ru(III)(2)(OH)(2)(cat)(2)(btpyan).
桥联配体 1,8-双(2,2':6',2''-三联吡啶-4'-基)蒽（btpyan）是通过蒽基-1,8-二硼酸与 4'-三氟甲基-2,2':6',2''-三联吡啶在 Pd(PPh(3))(4)（5 mol%）存在下的 Miyaura-Suzuki 交叉偶联反应合成的，产率为 68%。通过Ru(2)Cl(6)(btpyan)与相应儿茶酚的反应，制备了三种钌二氧杂环丁烷二聚体Ru(2)(OH)(2)(dioxolene)(2)(btpyan)（二氧杂环丁烷=3,6-二叔丁基-1,2-苯并二氢醌(1)、3,5-二氯-1,2-苯并二氢醌(2)和 4-硝基-1,2-苯并二氢醌(3))。1的电子结构由Ru(II)(2)(OH)(2)(sq)(2)(btpyan)（sq=半醌）近似表示。另一方面，2和3的电子态接近Ru(III)(2)(OH)(2)(cat)(2)(btpyan)（cat=儿茶酚），表明具有吸电子基团的二氧杂环丁烷稳定Ru(III)(2)(OH)(2)(cat)(2)(btpyan)而不是Ru(II)(2)(OH)(2)(sq)(2)(btpyan)作为共振异构体。没有发现1中羟基质子的去质子化迹象，而2和3在与 t-BuOLi 处理后并用 HClO(4)处理时表现出酸碱平衡。此外，在 pH 值为 4.0 时，在 ITO（氧化铟锡）电极上沉积的1的恒电位电解在比+1.6 V（相对于 SCE）更正的电位下催化 H(2)O 的四电子氧化以释放 O(2)。另一方面，在类似条件下，在 ITO 电极上沉积的2和3的电解没有显示出水氧化的催化活性。1、2和3之间这种反应性的差异归因于Ru(II)(2)(OH)(2)(sq)(2)(btpyan)和Ru(III)(2)(OH)(2)(cat)(2)(btpyan)之间共振平衡的移动。
