Redox properties of ruthenium nitrosyl porphyrin complexes with different axial ligation: structural, spectroelectrochemical (IR, UV-visible, and EPR), and theoretical studies.
Redox properties of ruthenium nitrosyl porphyrin complexes with different axial ligation: structural, spectroelectrochemical (IR, UV-visible, and EPR), and theoretical studies.
复制标题
不同轴向连接的钌亚硝酰卟啉配合物的氧化还原特性：结构、光谱电化学（红外、紫外-可见和 EPR）和理论研究。
作者：
Priti Singh;A. Das;B. Sarkar;M. Niemeyer;F. Roncaroli;J. Olabe;J. Fiedler;S. Záliš;W. Kaim
不同钌亚硝酰卟啉配合物 [(Por)Ru(NO)(X)] ( n+ ) （其中 Por (2-) = 四苯基卟啉二价阴离子 (TPP (2 (-) )）或八乙基卟啉二价阴离子 (OEP (2-)) 且 X = H 2O ( n = 1, 2, 3) 或吡啶， 4-氰基吡啶或 4-N,N-二甲基氨基吡啶 (n = 1, 0)) 的电子转移行为已有报道。 [(TPP)Ru(NO)(H 2O)]BF 4 的结构被确定为{MNO}物质，在178.1(3)度处具有几乎线性的RuNO排列。化合物[(Por)Ru(NO)(H 2O)]BF 4 经历两个可逆的单电子氧化过程。光谱电化学测量（IR、UV-vis-NIR 和 EPR）表明，第一次氧化发生在卟啉环上，这一点从诊断性卟啉自由基-阴离子振动带的出现可以明显看出（OEP (*-) 为 1530 cm (-1)，TPP (*-) 为 1290 cm (-1)），从大约 20 cm (-1) 的小位移 nu NO 和 g iso 约为 2.00 时的 EPR 信号。第二次氧化被发现对于 OEP 化合物是电化学可逆的，显示 nu NO 发生 55 cm (-1) 的位移，表明部分以金属为中心的过程。化合物 [(Por)Ru(NO)(X)]BF 4（其中 X = 吡啶）会发生可逆的单电子还原。通过光谱电化学研究确定还原位点以 NO 为中心，大约为 1。 nu NO 的-300 cm (-1) 偏移。 NO (*) 配合物的 EPR 响应基本上不受取代吡啶 X 变化的影响。DFT 计算支持对实验结果的解释，因为 [(TPP)Ru(NO)(X)] (+)（其中 X = H 2O 或吡啶）的 HOMO 经计算以卟啉 pi 系统为中心，而 [(TPP)Ru(NO)(X)] 的 LUMO (+) 具有大约 50% pi*(NO) 字符。这证实了 [(Por)Ru(NO)(H 2O)] (+) 的（第一次）氧化发生在卟啉环上，而 [(Por)Ru(NO)(X)] (+) 的还原主要以 NO 为中心，金属始终保持在低自旋钌 (II) 状态。 4% 吡啶对 [(TPP)Ru(NO)(py)] (+) LUMO 的贡献与还原形式的稳定性相关，而不是与水复合物的稳定性相关。
Experimental and computational results for different ruthenium nitrosyl porphyrin complexes [(Por)Ru(NO)(X)] ( n+ ) (where Por (2-) = tetraphenylporphyrin dianion (TPP (2 (-) )) or octaethylporphyrin dianion (OEP (2-)) and X = H 2O ( n = 1, 2, 3) or pyridine, 4-cyanopyridine, or 4- N,N-dimethylaminopyridine ( n = 1, 0)) are reported with respect to their electron-transfer behavior. The structure of [(TPP)Ru(NO)(H 2O)]BF 4 is established as an {MNO} species with an almost-linear RuNO arrangement at 178.1(3) degrees . The compound [(Por)Ru(NO)(H 2O)]BF 4 undergoes two reversible one-electron oxidation processes. Spectroelectrochemical measurements (IR, UV-vis-NIR, and EPR) indicate that the first oxidation occurs on the porphyrin ring, as evident from the appearance of diagnostic porphyrin radical-anion vibrational bands (1530 cm (-1) for OEP (*-) and 1290 cm (-1) for TPP (*-)), from the small shift of approximately 20 cm (-1) for nu NO and from the EPR signal at g iso approximately 2.00. The second oxidation, which was found to be electrochemically reversible for the OEP compound, shows a 55 cm (-1) shift in nu NO, suggesting a partially metal-centered process. The compounds [(Por)Ru(NO)(X)]BF 4, where X = pyridines, undergo a reversible one-electron reduction. The site of the reduction was determined by spectroelectrochemical studies to be NO-centered with a ca. -300 cm (-1) shift in nu NO. The EPR response of the NO (*) complexes was essentially unaffected by the variation in the substituted pyridines X. DFT calculations support the interpretation of the experimental results because the HOMO of [(TPP)Ru(NO)(X)] (+), where X = H 2O or pyridines, was calculated to be centered at the porphyrin pi system, whereas the LUMO of [(TPP)Ru(NO)(X)] (+) has about 50% pi*(NO) character. This confirms that the (first) oxidation of [(Por)Ru(NO)(H 2O)] (+) occurs on the porphyrin ring wheras the reduction of [(Por)Ru(NO)(X)] (+) is largely NO-centered with the metal remaining in the low-spin ruthenium(II) state throughout. The 4% pyridine contribution to the LUMO of [(TPP)Ru(NO)(py)] (+) is correlated with the stability of the reduced form as opposed to that of the aqua complex.