Porter Tyler M, Wang Jiaxi, Li Yingmin, Xiang Bo, Salsman Catherine, Miller Joel S, Xiong Wei, Kubiak Clifford P
Department of Chemistry and Biochemistry , University of California San Diego , 9500 Gilman Drive, La Jolla , California 92093-0358 , USA . Email:
Department of Chemistry , University of Utah , 315 South 1400 East, Room 2124 , Salt Lake City , Utah 84112-0850 , USA.
Chem Sci. 2018 Oct 8;10(1):113-117. doi: 10.1039/c8sc03258k. eCollection 2019 Jan 7.
Using a combination of two-dimensional infrared (2D IR) and variable temperature Fourier transform infrared (FTIR) spectroscopies the rapid structural isomerization of a five-coordinate ruthenium complex is investigated. In methylene chloride, three exchanging isomers were observed: (1) square pyramidal equatorial, (); (2) trigonal bipyramidal, (); and (3) square pyramidal apical, (). Exchange between and was found to be an endergonic process (Δ = 0.84 (0.08) kcal mol, Δ = 0.6 (0.4) eu) with an isomerization time constant of 4.3 (1.5) picoseconds (ps, 10 s). Exchange between and however was found to be exergonic (Δ = -2.18 (0.06) kcal mol, Δ = -5.3 (0.3) eu) and rate limiting with an isomerization time constant of 6.3 (1.6) ps. The trigonal bipyramidal complex was found to be an intermediate, with an activation barrier of 2.2 (0.2) kcal mol and 2.4 (0.2) kcal mol relative to the equatorial and apical square pyramidal isomers respectively. This study provides direct validation of the mechanism of Berry pseudorotation - the pairwise exchange of ligands in a five-coordinate complex - a process that was first described over fifty years ago. This study also clearly demonstrates that the rate of pseudorotation approaches the frequency of molecular vibrations.
结合二维红外（2D IR）和变温傅里叶变换红外（FTIR）光谱技术，对一种五配位钌配合物的快速结构异构化进行了研究。在二氯甲烷中，观察到三种相互转化的异构体：（1）赤道面为正方形的金字塔形，（ ）；（2）三角双锥形，（ ）；以及（3）顶点为正方形的金字塔形，（ ）。发现 和 之间的转化是一个吸能过程（Δ = 0.84 (0.08) kcal/mol，Δ = 0.6 (0.4) eu），异构化时间常数为4.3 (1.5) 皮秒（ps，10⁻¹² s）。然而， 和 之间的转化是放能的（Δ = -2.18 (0.06) kcal/mol，Δ = -5.3 (0.3) eu），且是限速步骤，异构化时间常数为6.3 (1.6) ps。发现三角双锥配合物是一种中间体，相对于赤道面和顶点正方形金字塔形异构体，其活化能垒分别为2.2 (0.2) kcal/mol和2.4 (0.2) kcal/mol。本研究直接验证了Berry假旋转机制——五配位配合物中配体的成对交换——这一过程早在五十多年前就已被描述。本研究还清楚地表明，假旋转速率接近分子振动频率。
