Direct observation of the intermediate in an ultrafast isomerization
Direct observation of the intermediate in an ultrafast isomerization
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直接观察超快异构化中的中间体
DOI：
10.1039/c8sc03258k
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发表时间：
2019
期刊：
影响因子：
8.4
通讯作者：
Kubiak, Clifford P.
中科院分区：
文献类型：
--
作者：
Porter, Tyler M.;Wang, Jiaxi;Li, Yingmin;Xiang, Bo;Salsman, Catherine;Miller, Joel S.;Xiong, Wei;Kubiak, Clifford P.
利用二维红外（2D IR）和变温傅里叶变换红外（FTIR）光谱相结合的方法研究了五坐标钌配合物的快速结构异构化。在二氯甲烷中，观察到三种交换异构体：(1)方锥体赤道，(1)；(2)三角双锥体，(0)；(3)方形锥顶，(2)。1和0之间的交换是一个内生过程(ΔH = 0.84 (0.08) kcal mol−1，ΔS = 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，0和2之间的交换被发现是exergonic (ΔH =−2.18 （0.06)kcal mol - 1， ΔS =−5.3 (0.3)eu）和速率限制，异构化时间常数为6.3 (1.6)ps。三角双锥体复合物被发现是一个中间产物，相对于赤道和顶端的方形锥体，其激活势垒分别为2.2 (0.2)kcal mol - 1和2.4 (0.2)kcal mol - 1。这项研究直接验证了Berry伪旋转的机制——五坐标配合物中配体的成对交换——这一过程在50多年前首次被描述。这项研究也清楚地表明，伪旋转的速率接近分子振动的频率。
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, (1); (2) trigonal bipyramidal, (0); and (3) square pyramidal apical, (2). Exchange between 1 and 0 was found to be an endergonic process (ΔH = 0.84 (0.08) kcal mol−1, ΔS = 0.6 (0.4) eu) with an isomerization time constant of 4.3 (1.5) picoseconds (ps, 10−12 s). Exchange between 0 and 2 however was found to be exergonic (ΔH = −2.18 (0.06) kcal mol−1, ΔS = −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−1 and 2.4 (0.2) kcal mol−1 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.