Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Inorg Chem. 2013 Jul 15;52(14):8250-63. doi: 10.1021/ic401170m. Epub 2013 Jul 3.
The aim of the present work was to check the suitability of dimolybdenum carboxylates, other than commonly used [Mo2(OAc)4], as auxiliary chromophores for determining the absolute configuration of optically active vic-diols by means of electronic circular dichroism (ECD). To this end, a set of dimolybdenum tetracarboxylates was synthesized, and subsequently, the two most promising compounds were selected, namely dimolybdenum tetrakis(μ-pivalate) and tetrakis(μ-isovalerate). The selection was based on their solubility in commonly used solvents, their stability in solution, their tolerance to air exposure, as well as their utility for dichroic studies. The stability of the obtained in situ chiral complexes was verified by measuring the dependence of ECD, UV-vis, and NMR spectra on time, temperature, and concentration. We have shown that the ECD spectra of diverse vic-diols with these complexes are suitable for configurational assignment based on the correlation between signs of Cotton effects (CEs) arising in the spectra and the stereostructure of the ligand. Furthermore, to aid in the interpretation of experimental results, a separate set of DFT calculations has been incorporated to provide additional insight into the structure of the chiral complexes involved. In contrast to the earlier assumptions, experiments showed that the chelating mode of ligation is preferred for the studied complexes.
本工作旨在检验二钼羧酸盐（除常用的 [Mo2(OAc)4] 外）作为辅助发色团，通过电子圆二色性（ECD）来确定手性邻二醇绝对构型的适用性。为此，合成了一组二钼四羧酸盐，随后选择了两种最有前途的化合物，即二钼四（μ-戊酸）和四（μ-异戊酸）。选择的依据是它们在常用溶剂中的溶解度、在溶液中的稳定性、对空气暴露的耐受性以及在二向色性研究中的实用性。通过测量 ECD、UV-vis 和 NMR 光谱随时间、温度和浓度的变化，验证了所得原位手性配合物的稳定性。我们表明，用这些配合物测定的各种邻二醇的 ECD 光谱适用于基于光谱中产生的Cotton 效应（CE）的符号与配体立体结构之间的相关性进行构象分配。此外，为了帮助解释实验结果，我们还进行了一组单独的 DFT 计算，以提供对所涉及的手性配合物结构的更多了解。与早期的假设相反，实验表明，对于所研究的配合物，螯合配位模式是首选的。
