Syntheses, characterization, and photo-hydrogen-evolving properties of tris(2,2'-bipyridine)ruthenium(II) derivatives tethered to a cis-Pt(II)Cl2 unit: insights into the structure-activity relationship.
Syntheses, characterization, and photo-hydrogen-evolving properties of tris(2,2'-bipyridine)ruthenium(II) derivatives tethered to a cis-Pt(II)Cl2 unit: insights into the structure-activity relationship.
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DOI：
10.1039/b617617h
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发表时间：
2007-03
影响因子：
4
通讯作者：
Hironobu Ozawa;Y. Yokoyama;Masa-aki Haga;K. Sakai
中科院分区：
文献类型：
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作者：
Hironobu Ozawa;Y. Yokoyama;Masa-aki Haga;K. Sakai
光放氢活性对三种不同的具有通式[（bpy）2 Ru]的Ru（II）Pt（II）二聚体进行了评价（增强水的光化学EDTA还原成分子氢的活性（微桥）PtCl 2]2+（bpy = 2，2 '-联吡啶;桥= 4，4 '-双（N-（3-氨基丙基）氨基甲酰基）-2，2'-联吡啶（L1），2，3-双（2-吡啶基）吡嗪（L2）和4，4 '-双（N-（4-吡啶基）甲基氨基甲酰基）-2，2'-联吡啶（L3）; EDTA =乙二胺四乙酸二钠盐）。合成并表征了一种新的钌铂配合物[（bpy）2 Ru（micro-L3）PtCl 2]2+。证实了所有三种化合物对于光化学H2产生都是无效的。在每种情况下，在Ar气氛下使用350-W氙灯光解含有Ru（II）Pt（II）二聚体和EDTA的乙酸盐缓冲溶液（pH = 5），在此期间通过气相色谱法分析放出的H2的量。通过将[Ru（bpy）3]2+和甲基紫精（N，N ′-二甲基-4，4 ′-联吡啶鎓）加入到上述光解溶液中进行另外的光解实验，以测试这些Ru（II）Pt（II）二聚体中涉及的Pt（II）单元的放H2活性。结果，发现L1和L2化合物中涉及的Pt（II）单元作为H2释放催化剂是活性的，而发现L3化合物中涉及的Pt（II）单元完全没有显示出活性。通过比较这些化合物和相关化合物的发光光谱，研究了[Ru（bpy）3]2+衍生物从3 MLCT激发态到束缚型Pt（II）催化剂中心的分子内电子转移猝灭程度.结果表明，在L1或L3化合物中，3 MLCT发光的猝灭根本没有增强。另一方面，L2化合物如先前报道的那样被强烈淬灭。除上述研究外，还研究了一些Pt（II）单体，顺式PtCl 2（NH 3）2，PtCl 2（en）（en =乙二胺），cis-PtCl 2（4-甲基吡啶）2，PtCl 2（2，2 '-联嘧啶），PtCl 2（4，4 '-二羧基-2，2'-联吡啶）和[PtCl（三联吡啶）]+（三次方= 2，2 '：6“，2”-三联吡啶），在EDTA，[Ru（bpy）3]2+和甲基紫精存在下进行了类似的研究，因为它们被认为是涉及L1-L3化合物的Pt（II）单元的结构类似物。具有顺式Pt（II）Cl 2单元的化合物通常被发现显示出高的H2释放活性。这被解释在负电荷的氯阴离子的连接导致的Pt（II）dz 2轨道负责的氢激活的不稳定。重要的是，顺式-PtCl 2（4-甲基吡啶）2表现出相对较高的活性作为H2-evolving催化剂，这表明的重要性的灵活旋转的吡啶基配体的有效氢活化在轴向位置的Pt（II）离子。DFT计算还显示了上述L3化合物的结构-活性关系的有效性。
The photo-hydrogen-evolving activity (activity to enhance the photochemical EDTA-reduction of water into molecular hydrogen) was evaluated for three different Ru(II)Pt(II) dimers with a general formula of [(bpy)2Ru(micro-bridge)PtCl2]2+(bpy = 2,2'-bipyridine; bridge = 4,4'-bis(N-(3-aminopropyl)carbamoyl)-2,2'-bipyridine (L1), 2,3-bis(2-pyridyl)pyrazine (L2), and 4,4'-bis(N-(4-pyridyl)methylcarbamoyl)-2,2'-bipyridine (L3); EDTA = ethylenediaminetetraacetic acid disodium salt). A new Ru(II)Pt(II) complex, [(bpy)2Ru(micro-L3)PtCl2]2+, was synthesized and characterized. It was confirmed that all three compounds are ineffective towards photochemical H2 production. In each case, an acetate-buffer solution (pH = 5) containing the Ru(II)Pt(II) dimer and EDTA was photolysed using a 350-W Xe lamp under an Ar atmosphere, during which the amount of H2 evolved was analysed by gas chromatography. Additional photolysis experiments were carried out by adding [Ru(bpy)3]2+ and methylviologen (N,N'-dimethyl-4,4'-bipyridinium) to the photolysis solutions described above to test the H2-evolving activity of the Pt(II) unit involved in these Ru(II)Pt(II) dimers. As a result, the Pt(II) units involved in the L1 and L2 compounds were found to be active as an H2-evolving catalyst, while that of the L3 compound was found to show no activity at all. The extent of intramolecular electron-transfer quenching from the 3MLCT excited state of the [Ru(bpy)3]2+ derivative to the tethering Pt(II) catalyst centre was investigated by comparison of the luminescence spectra of these compounds, together with the related compounds. The results showed that the quenching of the 3MLCT luminescence is not at all enhanced in either the L1 or the L3 compounds. On the other hand, the L2 compound is strongly quenched as previously reported. In addition to the above studies, the H2-evolving activity of some Pt(II) monomers, cis-PtCl2(NH3)2, PtCl2(en)(en = ethylenediamine), cis-PtCl2(4-methylpyridine)2, PtCl2(2,2'-bipyrimidine), PtCl2(4,4'-dicarboxy-2,2'-bipyridine), and [PtCl(terpy)]+(terpy = 2,2':6',2''-terpyridine), were similarly investigated in the presence of EDTA, [Ru(bpy)3]2+ and methylviologen, since they were regarded as structural analogues of the Pt(II) units involved in the L1-L3 compounds. The compounds having a cis-Pt(II)Cl2 unit were generally found to show high H2-evolving activity. This was interpreted in terms of the ligation of negatively charged chloride anions leading to the destabilization of the Pt(II) dz2 orbital responsible for the hydrogenic activation. Importantly, cis-PtCl2(4-methylpyridine)2 exhibited relatively high activity as an H2-evolving catalyst, suggesting the importance of the flexible rotation of the pyridyl ligands for efficient hydrogenic activation at the axial site of the Pt(II) ion. The DFT calculations also showed the validity of the structure-activity relationship discussed above for the L3 compound.