Catalysis of Mononuclear Aquaruthenium Complexes in Oxygen Evolution from Water: A New Radical Coupling Path using Hydroxocerium(IV) Species
Catalysis of Mononuclear Aquaruthenium Complexes in Oxygen Evolution from Water: A New Radical Coupling Path using Hydroxocerium(IV) Species
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DOI：
10.1002/asia.201000323
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发表时间：
2010-01-01
影响因子：
4.1
通讯作者：
Sakai, Ken
中科院分区：
文献类型：
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作者：
Yoshida, Masaki;Masaoka, Shigeyuki;Sakai, Ken
由一系列单核水钌配合物 [Ru(terpy)(bpy)(OH2)(2+)、[Ru-(tmtacn)(R(2)bpy)(OH2)(2+)（R = H、Me 和 OMe；R(2)bpy = 4,4'-二取代-2,2'-联吡啶）和 O-2 催化的机制研究了 [Ru(tpzm)-(R(2)bpy)(OH2)(2+)（R = H、Me 和 OMe），其中 terpy = 2,2':6',2 ''-三联吡啶，bpy = 2,2'-联吡啶，tmtacn = 1.,4,7-三甲基-1,4,7-三氮杂环壬烷，tpzm =三(1-吡唑基)甲烷。使用 Ce(NH4)(2)(NO3)(6) 作为氧化剂，研究了 O-2 释放动力学作为催化剂浓度或氧化剂浓度的函数；这些催化剂可分为两类，它们具有不同的 O-2 演化速率定律。在一类中，O-2 释放速率与催化剂和 Ce4+ 浓度呈线性关系，如 [Ru(terpy)(bpy)(OH2)](2+) 的简要报道（S. Masaoka, K. Sakai, Chem. Lett. 2009, 38, 182）。对于另一类，[Ru-(tmtacn)(R(2)bpy)(OH2)](2+)，O-2 释放速率与催化剂浓度成二次方，且与 Ce4+ 浓度无关。此外，通过实验和DFT研究实现了羟基铈(IV)离子的单线态双自由基特征。这些结果表明Ru-v=O物种的氧原子和羟基铈(IV)离子之间的自由基偶联是[Ru(terpy)(bpy)(OH2)](2+)和[Ru(tpzm)(R(2)bpy)(OH2)](2+)催化的关键步骤，而众所周知的两个Ru-v=O物种之间的氧代-氧代自由基偶联在催化中进行[Ru(tmtacn)(R(2)bpy)-(OH2)](2+)。这是第一份报告，证明羟基铈 (IV) 离子提供的自由基特性在此类钌络合物从水中演化出 O-2 的催化过程中发挥着至关重要的作用。
The mechanism of O-2 evolution from water catalyzed by a series of mononuclear aquaruthenium complexes, [Ru(terpy)(bpy)(OH2)(2+), [Ru-(tmtacn)(R(2)bpy)(OH2)(2+) (R = H, Me, and OMe; R(2)bpy = 4,4'-disubstituted-2,2'-bipyridines), and [Ru(tpzm)-(R(2)bpy)(OH2)(2+) (R = H, Me, and OMe), is investigated, where terpy = 2,2':6',2 ''-terpyridine, bpy = 2,2'-bipyridine, tmtacn = 1.,4,7-trimethyl-1,4,7-triazacyclononane, and tpzm = tris(1-pyrazolyl)methane. The kinetics of O-2 evolution is investigated as a function of either the catalyst concentration or the oxidant concentration by employing Ce(NH4)(2)(NO3)(6) as an oxidant; these catalysts can be classified into two groups that have different rate laws for O-2 evolution. In one class, the rate of O-2 evolution is linear to both the catalyst and Ce4+ concentrations, as briefly reported for [Ru(terpy)(bpy)(OH2)](2+) (S. Masaoka, K. Sakai, Chem. Lett. 2009, 38, 182). For the other class, [Ru-(tmtacn)(R(2)bpy)(OH2)](2+), the rate of O-2 evolution is quadratic to the catalyst concentration and independent of the Ce4+ concentration. Moreover, the singlet biradical character of the hydroxocerium(IV) ion was realized by experimental and DFT investigations. These results indicate that the radical coupling between the oxygen atoms of a Ru-v=O species and a hydroxocerium(IV) ion is the key step for the catalysis of [Ru(terpy)(bpy)(OH2)](2+) and [Ru(tpzm)(R(2)bpy)(OH2)](2+), while the well-known oxo-oxo radical coupling among two Ru-v=O species proceeds in the catalysis of [Ru(tmtacn)(R(2)bpy)-(OH2)](2+). This is the first report demonstrating that the radical character provided by the hydroxocerium(IV) ion plays a crucial role in the catalysis of such ruthenium complexes in the evolution of O-2 from water.