Institute of Chemical Research of Catalonia (ICIQ), Avinguda Paisos Catalans 16, E-43007 Tarragona, Spain.
J Am Chem Soc. 2009 Oct 28;131(42):15176-87. doi: 10.1021/ja9036127.
A thorough characterization of the Ru-Hbpp (in,in-{Ru(II)(trpy)(H(2)O)(mu-bpp)}(3+) (trpy is 2,2':6',2''-terpyridine, bpp is bis(2-pyridyl)-3,5-pyrazolate)) water oxidation catalyst has been carried out employing structural (single crystal X-ray), spectroscopic (UV-vis and NMR), kinetic, and electrochemical (cyclic voltammetry) analyses. The latter reveals the existence of five different oxidation states generated by sequential oxidation of an initial II,II state to an ultimate, formal IV,IV oxidation state. Each of these oxidation states has been characterized by UV-vis spectroscopy, and their relative stabilities are reported. The electron transfer kinetics for individual one-electron oxidation steps have been measured by means of stopped flow techniques at temperatures ranging from 10 to 40 degrees C and associated second-order rate constants and activation parameters (DeltaH() and DeltaS()) have been determined. Room-temperature rate constants for substitution of aqua ligands by MeCN as a function of oxidation state have been determined using UV-vis spectroscopy. Complete kinetic analysis has been carried out for the addition of 4 equiv of oxidant (Ce(IV)) to the initial Ru-Hbpp catalyst in its II,II oxidation state. Subsequent to reaching the formal oxidation state IV,IV, an intermediate species is formed prior to oxygen evolution. Intermediate formation and oxygen evolution are both much slower than the preceding ET processes, and both are first order with regard to the catalyst; rate constants and activation parameters are reported for these steps. Theoretical modeling at density functional and multireference second-order perturbation theory levels provides a microscopic mechanism for key steps in intermediate formation and oxygen evolution that are consistent with experimental kinetic data and also oxygen labeling experiments, monitored via mass spectrometry (MS), that unambiguously establish that oxygen-oxygen bond formation proceeds intramolecularly. Finally, the Ru-Hbpp complex has also been studied under catalytic conditions as a function of time by means of manometric measurements and MS, and potential deactivation pathways are discussed.
已经通过结构（单晶 X 射线）、光谱（紫外可见和 NMR）、动力学和电化学（循环伏安法）分析对 Ru-Hbpp（in,in-{Ru(II)(trpy)(H(2)O)(mu-bpp)}(3+)（trpy 是 2,2':6',2''-三联吡啶，bpp 是双（2-吡啶基）-3,5-吡唑））水氧化催化剂进行了全面表征。后者揭示了通过初始 II,II 态到最终的，形式上的 IV,IV 氧化态的连续氧化产生的五个不同的氧化态的存在。通过紫外可见光谱对每个氧化态进行了特征化，并报告了它们的相对稳定性。通过停流技术在 10 至 40 摄氏度的温度范围内测量了各个单电子氧化步骤的电子转移动力学，并确定了相关的二级速率常数和活化参数（DeltaH() 和 DeltaS()）。通过紫外可见光谱确定了作为氧化态函数的 Ru-Hbpp 催化剂中水配体被 MeCN 取代的室温速率常数。已经对初始 Ru-Hbpp 催化剂在其 II,II 氧化态下添加 4 当量氧化剂（Ce(IV)）的加成进行了完整的动力学分析。在达到形式氧化态 IV,IV 后，在氧气演化之前形成了一种中间物种。中间形成和氧气演化都比前面的 ET 过程慢得多，并且都与催化剂呈一级关系；报告了这些步骤的速率常数和活化参数。密度泛函和多参考二级微扰理论水平的理论建模为中间形成和氧气演化的关键步骤提供了微观机制，这些机制与实验动力学数据以及通过质谱（MS）监测的氧标记实验一致，这些实验明确地建立了氧-氧键的形成是分子内进行的。最后，还通过静态测量和 MS 作为时间函数在催化条件下研究了 Ru-Hbpp 络合物，讨论了潜在的失活途径。
