Zhang Hong-Tao, Su Xiao-Jun, Xie Fei, Liao Rong-Zhen, Zhang Ming-Tian
Center of Basic Molecular Science (CBMS), Department of Chemistry, Tsinghua University, Beijing, 100084, China.
Key Laboratory for Large-Format Battery Materials and System, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China.
Angew Chem Int Ed Engl. 2021 May 25;60(22):12467-12474. doi: 10.1002/anie.202100060. Epub 2021 Apr 28.
Herein, we report the importance of structure regulation on the O-O bond formation process in binuclear iron catalysts. Three complexes, [Fe (μ-O)(OH ) (TPA) ] (1), [Fe (μ-O)(OH ) (6-HPA)] (2) and [Fe (μ-O)(OH ) (BPMAN)] (3), have been designed as electrocatalysts for water oxidation in 0.1 M NaHCO solution (pH 8.4). We found that 1 and 2 are molecular catalysts and that O-O bond formation proceeds via oxo-oxo coupling rather than by the water nucleophilic attack (WNA) pathway. In contrast, complex 3 displays negligible catalytic activity. DFT calculations suggested that the anti to syn isomerization of the two high-valent Fe=O moieties in these catalysts takes place via the axial rotation of one Fe=O unit around the Fe-O-Fe center. This is followed by the O-O bond formation via an oxo-oxo coupling pathway at the Fe Fe state or via oxo-oxyl coupling pathway at the Fe Fe state. Importantly, the rigid BPMAN ligand in complex 3 limits the anti to syn isomerization and axial rotation of the Fe=O moiety, which accounts for the negligible catalytic activity.
在此，我们报道了双核铁催化剂中结构调控对O-O键形成过程的重要性。三种配合物，[Fe(μ-O)(OH)(TPA)] (1)、[Fe(μ-O)(OH)(6-HPA)] (2) 和 [Fe(μ-O)(OH)(BPMAN)] (3)，已被设计用作在0.1 M NaHCO溶液（pH 8.4）中进行水氧化的电催化剂。我们发现1和2是分子催化剂，且O-O键的形成是通过氧-氧偶联而非水亲核进攻（WNA）途径进行的。相比之下，配合物3显示出可忽略不计的催化活性。密度泛函理论计算表明，这些催化剂中两个高价Fe=O部分的反式到顺式异构化是通过一个Fe=O单元围绕Fe-O-Fe中心的轴向旋转发生的。随后在Fe-Fe状态下通过氧-氧偶联途径或在Fe-Fe状态下通过氧-氧自由基偶联途径形成O-O键。重要的是，配合物3中刚性的BPMAN配体限制了Fe=O部分的反式到顺式异构化和轴向旋转，这解释了其可忽略不计的催化活性。
