Noda Kyoko, Ohuchi Yuko, Hashimoto Akira, Fujiki Masayuki, Itoh Sumitaka, Iwatsuki Satoshi, Noda Toshiaki, Suzuki Takayoshi, Kashiwabara Kazuo, Takagi Hideo D
Graduate School of Science and Research Center for Materials Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8602, Japan.
Inorg Chem. 2006 Feb 6;45(3):1349-55. doi: 10.1021/ic051487l.
Controlled-potential electrochemical oxidation of cis-[Ru(ROCS2)2(PPh3)2] (R = Et, iPr) yielded corresponding Ru(III) complexes, and the crystal structures of cis-[Ru(ROCS2)2(PPh3)2] and trans-Ru(ROCS2)2(PPh3)2 were determined. Both pairs of complexes exhibited almost identical coordination structures. The Ru-P distances in trans-Ru(III)(ROCS2)2(PPh3)2 [2.436(3)-2.443(3) A] were significantly longer than those in cis-[Ru(II)(ROCS2)2(PPh3)2] [2.306(1)-2.315(2) A]: the smaller ionic radius of Ru(III) than that of Ru(II) stabilizes the trans conformation for the Ru(III) complex due to the steric requirement of bulky phosphine ligands while mutual trans influence by the phosphine ligands induces significant elongation of the Ru(III)-P bonds. Cyclic voltammograms of the cis-[Ru(ROCS2)2(PPh3)2] and trans-[Ru(ROCS2)2(PPh3)2]+ complexes in dichloromethane solution exhibited typical dual redox signals corresponding to the cis-Ru(ROCS2)2(PPh3)2 (ca. +0.15 and +0.10 V vs ferrocenium/ferrocene couple for R = Et and iPr, respectively) and to trans-Ru(ROCS2)2(PPh3)2 (-0.05 and -0.15 V vs ferrocenium/ferrocene for R = Et and iPr, respectively) couples. Analyses on the basis of the Nicholson and Shain's method revealed that the thermal disappearance rate of transient trans-[Ru(ROCS2)2(PPh3)2] was dependent on the concentration of PPh3 in the bulk: the rate constant for the intramolecular isomerization reaction of trans-[Ru(iPrOCS2)2(PPh3)2] was determined as 0.338 +/- 0.004 s(-1) at 298.3 K (deltaH* = 41.8 +/- 1.5 kJ mol(-1) and deltaS* = -114 +/- 7 J mol(-1) K(-1)), while the dissociation rate constant of coordinated PPh3 from the trans-[Ru(iPrOCS2)2(PPh3)2] species was estimated as 0.113 +/- 0.008 s(-1) at 298.3 K (deltaH* = 97.6 +/- 0.8 kJ mol(-1) and deltaS* = 64 +/- 3 J mol(-1) K(-1)), by monitoring the EC reaction (electrode reaction followed by chemical processes) at different concentrations of PPh3 in the bulk. It was found that the trans to cis isomerization reaction takes place via the partial dissociation of iPrOCS2(-) from Ru(II), contrary to the previous claim that it takes place by the twist mechanism.
顺式-[Ru(ROCS₂)₂(PPh₃)₂]（R = 乙基，异丙基）的控制电位电化学氧化产生了相应的Ru(III)配合物，并测定了顺式-[Ru(ROCS₂)₂(PPh₃)₂]和反式-Ru(ROCS₂)₂(PPh₃)₂的晶体结构。这两对配合物都表现出几乎相同的配位结构。反式-Ru(III)(ROCS₂)₂(PPh₃)₂中的Ru-P键长[2.436(3)-2.443(3) Å]明显长于顺式-[Ru(II)(ROCS₂)₂(PPh₃)₂]中的[2.306(1)-2.315(2) Å]：Ru(III)的离子半径小于Ru(II)，由于庞大膦配体的空间需求，使得Ru(III)配合物的反式构象更稳定，而膦配体之间的相互反式影响导致Ru(III)-P键显著伸长。顺式-[Ru(ROCS₂)₂(PPh₃)₂]和反式-[Ru(ROCS₂)₂(PPh₃)₂]+配合物在二氯甲烷溶液中的循环伏安图显示出典型的双氧化还原信号，分别对应于顺式-Ru(ROCS₂)₂(PPh₃)₂（对于R = 乙基和异丙基，相对于二茂铁鎓/二茂铁电对分别约为+0.15和+0.10 V）和反式-Ru(ROCS₂)₂(PPh₃)₂（对于R = 乙基和异丙基，相对于二茂铁鎓/二茂铁分别为-0.05和-0.15 V）电对。基于尼科尔森和沙因方法的分析表明，瞬态反式-[Ru(ROCS₂)₂(PPh₃)₂]的热消失速率取决于本体中PPh₃的浓度：在298.3 K时，反式-[Ru(异丙基OCS₂)₂(PPh₃)₂]分子内异构化反应的速率常数测定为0.338±0.004 s⁻¹（ΔH* = 41.8±1.5 kJ mol⁻¹，ΔS* = -114±7 J mol⁻¹ K⁻¹），而通过监测本体中不同浓度PPh₃的EC反应（电极反应后接化学过程），反式-[Ru(异丙基OCS₂)₂(PPh₃)₂]物种中配位PPh₃的解离速率常数在298.3 K时估计为0.113±0.008 s⁻¹（ΔH* = 97.6±0.8 kJ mol⁻¹，ΔS* = 64±3 J mol⁻¹ K⁻¹）。发现反式到顺式的异构化反应是通过iPrOCS₂⁻从Ru(II)的部分解离发生的，这与之前声称的通过扭转机制发生的说法相反。
