Mechanistic Insight into Reversible Core Structural Changes of Dinuclear μ-Hydroxoruthenium(II) Complexes with a 2,8-Di-2-pyridyl-1,9,10-anthyridine Backbone Prior to Water Oxidation Catalysis
Mechanistic Insight into Reversible Core Structural Changes of Dinuclear μ-Hydroxoruthenium(II) Complexes with a 2,8-Di-2-pyridyl-1,9,10-anthyridine Backbone Prior to Water Oxidation Catalysis
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水氧化催化前具有 2,8-Di-2-pyridyl-1,9,10-anthyridine 主链的双核 μ-羟基钌 (II) 配合物的可逆核心结构变化的机理洞察
DOI：
10.1021/acs.inorgchem.7b00978
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发表时间：
2017
影响因子：
4.6
通讯作者：
Yagi Masayuki
中科院分区：
文献类型：
--
作者：
Hirahara Masanari;Nagai Sho;Takahashi Kosuke;Watabe Shunsuke;Sato Taisei;Saito Kenji;Yui Tatsuto;Umemura Yasushi;Yagi Masayuki
近端，近端-(p,p)-[RuII2(tpy)2LXY]n+（tpy = 2,2 ';6 '，2″-三吡啶，L = 5-苯基-2,8-二-2-吡啶-1,9,10-anthyridine， X和Y =其他配位位点）得到了结构和功能上不同寻常的RuII(μ-OH) ruicore，它能够催化水氧化，关键水插入到核心（Inorg）。现年54岁的Chem.2015 7627)。本文研究了p，p-[Ru2(tpy)2L(μ-Cl)]3+(Ru2(μ-Cl))、p,p-[Ru2(tpy)2L(μ-OH)]3+(Ru2(μ-OH))、p,p-[Ru2(tpy)2L(OH)(OH2)]3+(Ru2（OH)(OH2)）和p-[Ru2(tpy)2L(OH)2]2+(Ru2(OH)2)在水溶液中的桥接配体取代序列。Ru2（μ-Cl）缓慢转化为（10-4s-1） toRu2(μ-OH)，而Ru2（μ-OH）在加入水后转化为非常缓慢（10-6s-1） toRu2(OH)(OH2)，在pH为8.5 ~ 12.3时达到平衡。基于密度泛函理论（DFT）计算，Ru2(OH)（OH2）的热力学稳定性比toRu2（μ-OH）高13.3 kJ mol-1in水，这是由于其核心结构通过水键、氢键和L主配体的多重氢键相互作用而特别稳定。在10 ~ 100 mM范围内，OH离子插入ru2 (μ-OH)toRu2(OH)2的速率随着OH浓度的增加而线性增加。在pH为8.5 ~ 12.3的水溶液中，水插入到核心的速度非常慢（~ 10 - 6s - 1），而在pH为13.4以上，OH离子的插入速度加快了2个数量级（10 - 5 - 10 - 4s - 1）。包括活化参数在内的动力学数据表明，pH为8.5 ~ 12.3时，水与ru2 （μ-OH）的RuII(μ-OH) ruicore的结合机制改变了pH为13.4以上时oh离子向核心插入的交换机制，因为oh离子的亲核攻击相对较强。结果表明，Ru2（μ-OH）和Ru2(OH)（OH2）质子化生成的p，p-[Ru2(tpy)2L(μ-OH2)]4+与toRu2（μ-OH）和Ru2(OH)（OH2）质子化生成的p，p-[Ru2(tpy)2L(OH2)2]4+的不稳定性分别为71.3和112.4 kJ mol - 1。Ru2（μ-OH）、Ru2(OH)（OH2）和Ru2(OH)2toRu2（μ-Cl）的逆反应是通过μ-OH或OH配体的质子化作用降低核心电荷引起的。
proximal,proximal-(p,p)-[RuII2(tpy)2LXY]n+(tpy = 2,2′;6′,2″-terpyridine, L = 5-phenyl-2,8-di-2-pyridyl-1,9,10-anthyridine, and X and Y = other coordination sites) yields the structurally and functionally unusual RuII(μ-OH)RuIIcore, which is capable of catalyzing water oxidation with key water insertion to the core (Inorg. Chem.2015,54, 7627). Herein, we studied a sequence of bridging-ligand substitution amongp,p-[Ru2(tpy)2L(μ-Cl)]3+(Ru2(μ-Cl)),p,p-[Ru2(tpy)2L(μ-OH)]3+(Ru2(μ-OH)),p,p-[Ru2(tpy)2L(OH)(OH2)]3+(Ru2(OH)(OH2)), andp,p-[Ru2(tpy)2L(OH)2]2+(Ru2(OH)2) in aqueous solution.Ru2(μ-Cl)converted slowly (10–4s–1) toRu2(μ-OH), and furtherRu2(μ-OH)converted very slowly (10–6s–1) toRu2(OH)(OH2)by the insertion of water to reach equilibrium at pH 8.5–12.3. On the basis of density functional theory (DFT) calculations,Ru2(OH)(OH2)was predicted to be thermodynamically stable by 13.3 kJ mol–1in water compared toRu2(μ-OH)because of the specially stabilized core structure by multiple hydrogen-bonding interactions involving aquo, hydroxo, and L backbone ligands. The observed rate fromRu2(μ-OH)toRu2(OH)2by the insertion of an OH–ion increased linearly with an increase in the OH–concentration from 10 to 100 mM. The water insertion to the core is very slow (∼10–6s–1) in aqueous solution at pH 8.5–12.3, whereas the insertion of OH–ions is accelerated (10–5–10–4s–1) above pH 13.4 by 2 orders of magnitude. The kinetic data including activation parameters suggest that the associative mechanism for the insertion of water to the RuII(μ-OH)RuIIcore ofRu2(μ-OH)at pH 8.5–12.3 alters the interchange mechanism for the insertion of an OH–ion to the core above pH 13.4 because of relatively stronger nucleophilic attack of OH–ions. The hypothesizedp,p-[Ru2(tpy)2L(μ-OH2)]4+andp,p-[Ru2(tpy)2L(OH2)2]4+formed by protonation fromRu2(μ-OH)andRu2(OH)(OH2)were predicted to be unstable by 71.3 and 112.4 kJ mol–1compared toRu2(μ-OH)andRu2(OH)(OH2), respectively. The reverse reactions ofRu2(μ-OH),Ru2(OH)(OH2), andRu2(OH)2toRu2(μ-Cl)below pH 5 could be caused by lowering the core charge by protonation of the μ-OH–or OH–ligand.