Department of Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
Inorg Chem. 2013 Mar 4;52(5):2505-18. doi: 10.1021/ic302446h. Epub 2013 Feb 14.
Mononuclear Ru-based water oxidation catalysts containing anionic ancillary ligands have shown promising catalytic efficiency and intriguing properties. However, their insolubility in water restricts a detailed mechanism investigation. In order to overcome this disadvantage, complexes Ru(II)(bpc)(bpy)OH2 (1(+), bpc = 2,2'-bipyridine-6-carboxylate, bpy = 2,2'-bipyridine) and Ru(II)(bpc)(pic)3 (2(+), pic = 4-picoline) were prepared and fully characterized, which features an anionic tridentate ligand and has enough solubility for spectroscopic study in water. Using Ce(IV) as an electron acceptor, both complexes are able to catalyze O2-evolving reaction with an impressive rate constant. On the basis of the electrochemical and kinetic studies, a water nucleophilic attack pathway was proposed as the dominant catalytic cycle of the catalytic water oxidation by 1(+), within which several intermediates were detected by MS. Meanwhile, an auxiliary pathway that is related to the concentration of Ce(IV) was also revealed. The effect of anionic ligand regarding catalytic water oxidation was discussed explicitly in comparison with previously reported mononuclear Ru catalysts carrying neutral tridentate ligands, for example, 2,2':6',2″-terpyridine (tpy). When 2(+) was oxidized to the trivalent state, one of its picoline ligands dissociated from the Ru center. The rate constant of picoline dissociation was evaluated from time-resolved UV-vis spectra.
单核钌基水氧化催化剂含有阴离子辅助配体，具有有前景的催化效率和有趣的性质。然而，它们在水中的不溶性限制了对详细机制的研究。为了克服这一缺点，制备了配合物Ru(II)(bpc)(bpy)OH2（1(+)，bpc = 2,2'-联吡啶-6-羧酸，bpy = 2,2'-联吡啶）和Ru(II)(bpc)(pic)3（2(+)，pic = 4-吡啶），其特征是阴离子三齿配体，并且在水中具有足够的溶解度用于光谱研究。使用 Ce(IV) 作为电子受体，这两种配合物都能够以令人印象深刻的速率常数催化 O2 析出反应。基于电化学和动力学研究，提出了水亲核进攻途径作为 1(+)催化水氧化的主要催化循环，其中通过 MS 检测到了几个中间体。同时，还揭示了与 Ce(IV)浓度相关的辅助途径。通过与之前报道的带有中性三齿配体的单核 Ru 催化剂（例如 2,2':6',2″-三联吡啶（tpy））进行比较，明确讨论了阴离子配体对催化水氧化的影响。当 2(+)被氧化为三价态时，其一个吡啶配体从 Ru 中心解离。从时间分辨紫外-可见光谱评估了吡啶配体解离的速率常数。
