Aimoto Yutaro, Parent Alexander R, Yamauchi Kosei, Sakai Ken
Department of Chemistry, Faculty of Science, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan.
Department of Chemistry and Biochemistry, North Dakota State University, P.O. Box 6050, Fargo, North Dakota 58108-6050, United States.
J Am Chem Soc. 2024 Jun 6. doi: 10.1021/jacs.4c05389.
Water oxidation is a key to achieving sustainable energy cycles, for which higher-valent metal-oxo species often play a key role to accelerate the rate-limiting O-O bond formation. The present study undertook efforts to clarify one of the steps postulated for the water oxidation (WO) catalyzed by [Ru(terpy)(bpy)(OH)] (terpy = 2,2':6',6″-terpyridine, bpy = 2,2'-bipyridine). This study focuses on inner-sphere electron transfer for the Ce-driven oxidation of the Ru═O species into the Ru═O species. The approach to this step became possible by inventing a feasible method to isolate an air-stable Ru═O powder sample in this work. Importantly, by mixing the thus-obtained Ru═O sample with CAN (cerium ammonium nitrate), the inner-sphere adduct [Ru(═O)(terpy)(bpy)][Ce(NO)(OH)] was successfully isolated. The IR spectrum of the isolated adduct exhibits a strong band at 774 cm attributable to the Ru═O-Ce stretching vibration, proving covalent bonding of the oxo to the Ce center. Furthermore, the absorption spectrum of this greenish black powder shows a broad absorption band at 600 nm, suggesting a charge transfer transition from the π* orbital of Ru═O to the 4f orbital of Ce, as supported by TD-DFT calculations. The addition of one equivalent of CAN to the Ru═O solution induces the spectral change due to formation of the 1:1 adduct identical to the isolated adduct. Our study provides a clue to the formation of an inner-sphere adduct having a Ru═O-Ce core in the Ce-driven WO catalysis.
水氧化是实现可持续能源循环的关键，高价金属氧物种通常在加速限速的O-O键形成过程中发挥关键作用。本研究致力于阐明由[Ru(terpy)(bpy)(OH)]（terpy = 2,2':6',6″-三联吡啶，bpy = 2,2'-联吡啶）催化的水氧化（WO）假定步骤之一。本研究聚焦于Ce驱动的Ru═O物种氧化为Ru═O物种的内球电子转移。通过发明一种可行的方法来分离空气稳定的Ru═O粉末样品，得以研究这一步骤。重要的是，通过将如此获得的Ru═O样品与硝酸铈铵（CAN）混合，成功分离出内球加合物[Ru(═O)(terpy)(bpy)][Ce(NO)(OH)]。分离出的加合物的红外光谱在774 cm处显示出一个强峰，归因于Ru═O-Ce伸缩振动，证明了氧与Ce中心的共价键合。此外，这种绿黑色粉末的吸收光谱在600 nm处显示出一个宽吸收带，表明从Ru═O的π*轨道到Ce的4f轨道的电荷转移跃迁，TD-DFT计算支持这一点。向Ru═O溶液中加入一当量的CAN会由于形成与分离出的加合物相同的1:1加合物而引起光谱变化。我们的研究为Ce驱动的WO催化中具有Ru═O-Ce核心的内球加合物的形成提供了线索。
