Department of Chemistry, University of California-Davis, Davis, California 95616, United States.
J Am Chem Soc. 2012 Dec 12;134(49):19973-6. doi: 10.1021/ja3093532. Epub 2012 Dec 3.
At high concentrations, nitrate ion alters the dynamics of ruthenium "blue dimer"-catalyzed water oxidation by Ce(IV) such that the oxidation rate is enhanced and a unique reaction intermediate accumulates. This intermediate is characterized by distinct EPR, optical, and resonance Raman (RR) spectra, with the appearance in the latter of a new oxygen isotope-sensitive band. Both Ce(IV) and nitrate are required to generate this intermediate, which suggests ceric-nitrate complexes as the causative agents. Use of (18)O-labeled and (15)N-labeled materials has established that (1) the new RR band is not an O-O stretching mode (for example, as might be associated with a peroxo species) but involves the O atom coordinated to a Ru center, and (2) the O(2) product does not contain an O atom derived from nitrate, eliminating several plausible pathways involving O-atom transfer to oxidized dimer. Although these results are surprising, similar phenomena have been reported for water oxidation catalyzed by monomeric Ru complexes. The dramatic effects observed for the "blue dimer" make it an ideal candidate for further study.
在高浓度下，硝酸根离子改变了铈（IV）催化的钌“蓝色二聚体”水氧化反应的动力学，从而提高了氧化速率，并积累了一种独特的反应中间体。这种中间体具有独特的 EPR、光学和共振拉曼（RR）光谱，在后者中出现了一个新的氧同位素敏感带。Ce(IV)和硝酸盐都需要生成这种中间体，这表明铈-硝酸盐配合物是致病剂。使用（18）O 标记和（15）N 标记的材料已经确定：（1）新的 RR 带不是 O-O 伸缩模式（例如，可能与过氧物种有关），而是涉及与 Ru 中心配位的 O 原子，并且（2）O2 产物不包含源自硝酸盐的 O 原子，排除了几种涉及向氧化二聚体转移 O 原子的合理途径。尽管这些结果令人惊讶，但已报道类似的现象也存在于单核 Ru 配合物催化的水氧化反应中。“蓝色二聚体”观察到的剧烈影响使其成为进一步研究的理想候选物。
