Steric and electronic control of an ultrafast isomerization
Steric and electronic control of an ultrafast isomerization
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超快异构化的空间和电子控制
DOI：
10.1039/c9sc02359c
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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.;Ostericher, Andrew L.;Kubiak, Clifford P.
本文报道了空间和电子因素对五配位钌二烯配合物Ru((CF3)2C2S2)(CO)(L)2 （L =单齿膦配体）超快（皮秒）异构化影响的合成控制。制备了7种新的钌二硫烯配合物，并用单晶x射线衍射对其进行了表征。这些配合物都是方锥体，只是羰基配体的轴向配位和赤道配位不同。傅里叶变换红外光谱（FTIR）研究了溶液中配合物的ν(CO)波段，这些波段显示了每个配合物的两个或三个异构体之间的快速交换。异构化被提出遵循类似Berry的伪旋化机制，其中亚稳的三角双锥体（TBP）中间体在光谱上被观察到。在等锥角下，电子调谐膦配体L = PPh3， P((P - me)Ph)3, ((P - cl)Ph)3对不同取代配合物的轴向、赤道和TBP异构体的动力学和热力学稳定性影响不大。在磷化氢锥角范围内（135 < θ < 165°），磷化氢配体的立体调谐对异构化过程有深远的影响，在最大立体体积的极限下，轴向异构体是观察不到的。利用红外光谱的温度依赖性获得了七种二硫代钌配合物不同异构体的相对热力学稳定性。本研究详细介绍了配体空间效应如何在皮秒时间尺度上指导能量小于2.2 kcal mol−1的离散异构体的溶液状态动力学。这项工作为过渡金属配合物基态的超快异构化提供了迄今为止最详细的描述。
Synthetic control of the influence of steric and electronic factors on the ultrafast (picosecond) isomerization of penta-coordinate ruthenium dithietene complexes (Ru((CF3)2C2S2)(CO)(L)2, where L = a monodentate phosphine ligand) is reported. Seven new ruthenium dithietene complexes were prepared and characterized by single crystal X-ray diffraction. The complexes are all square pyramidal and differ only in the axial vs. equatorial coordination of the carbonyl ligand. Fourier Transform Infrared (FTIR) spectroscopy was used to study the ν(CO) bandshapes of the complexes in solution, and these reveal rapid exchange between two or three isomers of each complex. Isomerization is proposed to follow a Berry psuedorotation-like mechanism where a metastable, trigonal bipyramidal (TBP) intermediate is observed spectroscopically. Electronic tuning of the phosphine ligands L = PPh3, P((p-Me)Ph)3, ((p-Cl)Ph)3, at constant cone angle is found to have little effect on the kinetics or thermodynamic stabilities of the axial, equatorial and TBP isomers of the differently substituted complexes. Steric tuning of the phosphine ligands over a range of phosphine cone angles (135 < θ < 165°) has a profound impact on the isomerization process, and in the limit of greatest steric bulk, the axial isomer is not observable. Temperature dependence of the FTIR spectra was used to obtain the relative thermodynamic stabilities of the different isomers of each of the seven ruthenium dithietene complexes. This study details how ligand steric effects can be used to direct the solution state dynamics on the picosecond time scale of discrete isomers energetically separated by <2.2 kcal mol−1. This work provides the most detailed description to date of ultrafast isomerization in the ground states of transition metal complexes.