Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.
Dalton Trans. 2018 Nov 22;47(45):16337-16349. doi: 10.1039/c8dt03183e.
A series of copper complexes bearing polypyridyl tridentate ligands have been prepared to fine tune their reactivity toward the oxygen reduction reaction (ORR). During the process of preparation of our copper complexes, we successfully obtained two new crystal structures which are Cu2(μ-Cl)2(adpa)22 (2b) and Cu2(addpa)(CH3CN)2(ClO4)22 (3a) and a new structure Cu2(addpa)(CH3CN)2(H2O)24 (3b) captured after the catalytic ORR. Electrochemical studies and stoichiometric chemical reduction of copper(ii) complexes by ascorbic acid indicated that the presence of an anthracene unit helps to facilitate the reduction of Cu(ii) as well as the stabilisation of Cu(i) species. Regarding oxygen activation, the dinuclear Cu(i) complex 3a showed significantly higher ORR activity than its analogous mononuclear complex 2a. Complex 3a was also found to be relatively robust and competent in catalytic O2 reduction. The observed H2O2 product after this catalysis, together with the data obtained from DFT calculations supported that 3a exhibited a 2H+, 2e- catalytic activity towards the ORR as opposed to the expected 4H+, 4e- process usually found in copper complexes with tridentate ligands. The proton (H+) source for this process was expected from ascorbic acid which also serves as a reducing agent in this reaction. This work highlighted an approach for tuning the ORR activity of the copper complexes by the introduction of a conjugated-π moiety to the supporting ligand.
一系列含有多吡啶三齿配体的铜配合物已被制备出来，以微调其对氧还原反应（ORR）的反应性。在我们的铜配合物的制备过程中，我们成功地获得了两个新的晶体结构，即Cu2(μ-Cl)2(adpa)22（2b）和Cu2(addpa)(CH3CN)2(ClO4)22（3a），以及在催化 ORR 后捕获的新结构Cu2(addpa)(CH3CN)2(H2O)24（3b）。电化学研究和抗坏血酸对铜（ii）配合物的化学计量还原表明，蒽单元的存在有助于促进 Cu(ii)的还原以及 Cu(i)物种的稳定。关于氧活化，双核 Cu(i)配合物 3a 显示出比其类似的单核配合物 2a 更高的 ORR 活性。还发现配合物 3a 在催化 O2 还原方面相对稳健和有能力。在这种催化作用后观察到的 H2O2 产物，以及从 DFT 计算获得的数据表明，3a 表现出对 ORR 的 2H+，2e-催化活性，而不是通常在具有三齿配体的铜配合物中发现的预期 4H+，4e-过程。这个过程的质子（H+）来源预计来自抗坏血酸，它也是该反应中的还原剂。这项工作强调了通过向支撑配体中引入共轭-π 部分来调谐铜配合物的 ORR 活性的方法。
