Cooperative Effects of Heterodinuclear IrIII-MII Complexes on Catalytic H2 Evolution from Formic Acid Dehydrogenation in Water
Cooperative Effects of Heterodinuclear IrIII-MII Complexes on Catalytic H2 Evolution from Formic Acid Dehydrogenation in Water
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DOI：
10.1021/acs.inorgchem.0c00812
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发表时间：
2020-09-08
影响因子：
4.6
通讯作者：
Kojima, Takahiko
中科院分区：
文献类型：
--
作者：
Hong, Dachao;Shimoyama, Yoshihiro;Kojima, Takahiko
以3，5-二（2-吡啶基）吡唑（Hbpp）为结构导向配体，合成了具有两个相邻反应位的新型异双核Ir-III-M-II配合物（M = Co，Ni或Cu），并将其用作甲酸脱氢反应的催化剂.的异金属中心的合作效应，观察到在H-2的演变与相应的单核Ir-III和M-II配合物的Ir-III-M-II配合物的组分相比。Ir-III-M-II复合物的H-2释放速率最多为单核Ir-III复合物的350倍。催化活性的大小顺序为：Ir-III-Cu-II络合物<（IrCoII）-Co-III络合物< Ir-III-Ni-II络合物。通过紫外可见光谱、H-1核磁共振谱和电喷雾飞行时间质谱（ESI-TOF-MS）等手段，成功地检测到了Ir-III-M-II配合物的Ir-III-H中间体。Ir-III-M-II配合物对H-2释放的催化增强作用表明，Ir-III部分中形成的Ir-III-H物种作为反应物种，M-II部分通过桥连bpp配体从M-II中心到Ir-III中心的电子效应作为加速位点。Ir-III-M-II配合物也可以在3d M-II中心激活H2O作为质子源以促进H-2的释放。此外，在Michaelis-Menten图的基础上研究了甲酸对Ir-III-M-II络合物的亲和力; Ir-III-Co-II和Ir-III-Ni-II络合物表现出的亲和力相对高于Ir-III-Cu-II络合物。通过反应中间体的光谱检测、动力学分析和同位素标记实验，揭示了Ir-III-M-II配合物的催化放氢机理。
Novel heterodinuclear Ir-III-M-II complexes (M = Co, Ni, or Cu) with two adjacent reaction sites were synthesized by using 3,5-bis(2-pyridyl)-pyrazole (Hbpp) as a structure-directing ligand and employed as catalysts for H-2 evolution through formic acid dehydrogenation in water. A cooperative effect of the hetero-metal centers was observed in the H-2 evolution in comparison with the corresponding mononuclear Ir-III and M-II complexes as the components of the Ir-III-M-II complexes. The H-2 evolution rate for the Ir-III-M-II complexes was at most 350-fold higher than that of the mononuclear Ir-III complex. The catalytic activity increased in the following order: Ir-III-Cu-II complex < (IrCoII)-Co-III complex < Ir-III-Ni-II complex . The Ir-III-H intermediates of the Ir-III-M-II complexes were successfully detected by ultravioletvisible, H-1 nuclear magnetic resonance, and ESI-TOF-MS spectra. The catalytic enhancement of H-2 evolution by the Ir-III-M-II complexes indicates that the Ir-III-H species formed in the Ir-III moiety act as reactive species and the M-II moieties act as acceleration sites by the electronic effect from the M-II center to the Ir-III center through the bridging bpp ligand. The Ir-III-M-II complexes may also activate H2O at the 3d M-II centers as a proton source to facilitate H-2 evolution. In addition, the affinity of formate for the Ir-III-M-II complexes was investigated on the basis of Michaelis-Menten plots; the Ir-III-Co-II and Ir-III-Ni-II complexes exhibited affinities that were relatively higher than that of the Ir-III-Cu-II complex. The catalytic mechanism of H-2 evolution by the Ir-III-M-II complexes was revealed on the basis of spectroscopic detection of reaction intermediates, kinetic analysis, and isotope labeling experiments.