Department of Chemistry, University of Zurich , Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Paul Scherrer Institute , CH-5232 Villigen PSI, Switzerland.
J Am Chem Soc. 2017 Oct 11;139(40):14198-14208. doi: 10.1021/jacs.7b07361. Epub 2017 Sep 27.
The future of artificial photosynthesis depends on economic and robust water oxidation catalysts (WOCs). Cobalt-based WOCs are especially promising for knowledge transfer between homogeneous and heterogeneous catalyst design. We introduce the active and stable {CoO} cubane Co(dpy{OH}O)(OAc)(HO) (CoO-dpk) as the first molecular WOC with the characteristic {HO-Co(OR)-OH} edge-site motif representing the sine qua non moiety of the most efficient heterogeneous Co-oxide WOCs. DFT-MD modelings as well as in situ EXAFS measurements indicate the stability of the cubane cage in solution. The stability of CoO-dpk under photocatalytic conditions ([Ru(bpy)]/SO) was underscored with a wide range of further analytical methods and recycling tests. FT-IR monitoring and HR-ESI-MS spectra point to a stable coordination of the acetate ligands, and DFT-MD simulations along with H/H exchange experiments highlight a favorable intramolecular base functionality of the dpy{OH}O ligands. All three ligand types enhance proton mobility at the edge site through a unique bioinspired environment with multiple hydrogen-bonding interactions. In situ XANES experiments under photocatalytic conditions show that the {CoO} core undergoes oxidation to Co(III) or higher valent states, which recover rather slowly to Co(II). Complementary ex situ chemical oxidation experiments with [Ru(bpy)] furthermore indicate that the oxidation of all Co(II) centers of CoO-dpk to Co(III) is not a mandatory prerequisite for oxygen evolution. Moreover, we present the CoNi(dpy{OH}O)(OAc)(HO) (CoNiO-dpk) series as the first mixed Co/Ni-cubane WOCs. They newly bridge homogeneous and heterogeneous catalyst design through fine-tuned edge-site environments of the Co centers.
人工光合作用的未来取决于经济且坚固的水氧化催化剂 (WOC)。基于钴的 WOC 特别有希望在均相和多相催化剂设计之间进行知识转移。我们引入了活性和稳定的 {CoO} 立方烷 Co(dpy{OH}O)(OAc)(HO) (CoO-dpk)，作为具有特征 {HO-Co(OR)-OH} 边缘位点基元的第一个分子 WOC，该基元是最有效的多相 Co 氧化物 WOC 的必要组成部分。DFT-MD 建模以及原位 EXAFS 测量表明立方烷笼在溶液中的稳定性。通过广泛的其他分析方法和回收测试，强调了 CoO-dpk 在光催化条件下 ([Ru(bpy)]/SO) 的稳定性。FT-IR 监测和 HR-ESI-MS 谱表明，醋酸盐配体的配位稳定，DFT-MD 模拟和 H/H 交换实验突出了 dpy{OH}O 配体有利的分子内碱基功能。这三种配体类型都通过独特的具有多个氢键相互作用的仿生环境增强了边缘位点的质子迁移率。在光催化条件下进行的原位 XANES 实验表明，{CoO} 核经历氧化为 Co(III) 或更高价态，然后缓慢恢复为 Co(II)。用 [Ru(bpy)] 进行的补充的非原位化学氧化实验进一步表明，CoO-dpk 中所有 Co(II) 中心氧化为 Co(III) 不是氧析出的强制性前提条件。此外，我们提出了 CoNi(dpy{OH}O)(OAc)(HO) (CoNiO-dpk) 系列作为第一个混合 Co/Ni 立方烷 WOC。它们通过精细调整 Co 中心的边缘位点环境，新的桥接了均相和多相催化剂设计。
