Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
J Am Chem Soc. 2017 Jul 12;139(27):9108-9111. doi: 10.1021/jacs.7b03044. Epub 2017 Jun 27.
Toward the development of structural and functional models of the oxygen evolving complex (OEC) of photosystem II, we report the synthesis of site-differentiated tetranuclear manganese complexes featuring three six-coordinate and one five-coordinate Mn centers. To incorporate biologically relevant second coordination sphere interactions, substituents capable of hydrogen bonding are included as pyrazolates with arylamine substituents. Complexes with terminal anionic ligands, OH or Cl, bound to the lower coordinate metal center are supported through the hydrogen-bonding network in a fashion reminiscent of the enzymatic active site. The hydroxide complex was found to be a competent electrocatalyst for O-O bond formation, a key transformation pertinent to the OEC. In an acetonitrile-water mixture, at neutral pH, electrochemical water oxidation to hydrogen peroxide was observed, albeit with low (15%) Faradaic yield, likely due to competing reactions with organics. In agreement, 9,10-dihydroanthracene is electrochemically oxidized in the presence of this cluster both via H-atom abstraction and oxygenation with ∼50% combined Faradaic yield.
为了开发光合作用系统 II 中氧析出复合物（OEC）的结构和功能模型，我们报告了合成具有三个六配位和一个五配位 Mn 中心的位分辨四核锰配合物。为了纳入生物学上相关的第二配位层相互作用，包含了能够形成氢键的取代基，如带有芳胺取代基的吡唑盐。通过氢键网络，将带有终端阴离子配体 OH 或 Cl 的配合物与下配位金属中心结合，这一方式让人联想到酶的活性位点。该氢氧化物配合物被发现是 O-O 键形成的有效电催化剂，这是与 OEC 相关的关键转化。在中性 pH 的乙腈-水混合物中，观察到电化学水氧化生成过氧化氢，但法拉第产率低（15%），这可能是由于与有机物的竞争反应所致。一致地，在该配合物存在下，9,10-二氢蒽通过 H 原子的攫取和氧合以约 50%的总法拉第产率进行电化学氧化。
