Theoretical Studies On The Structural Relation Of Chiroptical Properties Of Transition Metal Chelates

Many transition-metal complexes with organic ligands possess the characteristics of optical activity as well as the ability of non-symmetric catalyst due to their abundant chiral arrays. These characteristics make them be both ideal models for the study of structure-chiroptical properties, and powerful probes for the chiral discinmination of bio-and medicine macromolecules. Especially in the recent decades, the relevant researches have become a hot-subject in both scientific and industrial domains due to the demands of exploring new non-symmetric catalysts and new chiral medicines.Since Werner first pointed out that the chirality of metal complexes is originated from the non-symmetric steric arrangement of the ligands in 1911, it has been expected that the chiral arrarys, such as the△/Λconfigurations at the octahedral core, theδ/λtwists of the rings, and the R/S carbon atoms at the substituted ligand ring etc. are responsible for the chiroptical properties. To reveal the relationships between chiroptical properties and molecular structures, much work has been done experimentally and theoretically. To reveal the relationships between chiroptical properties and molecular structures, much work has been done experimentally and theoretically. However, no overal pictures for the individual contributions of different chiral arrays to the circular dichroism (CD) spectra of chiral molecules were established due to the difficulty in quantitatively calculating CD spectra during that time.In order to solve this problem, the chiroptical properties of tris-diamine ruthenium and coblat chelates have been systematically investigated in this paper, and the relationships between the chiroptical properties and the chiral arrays have been revealed. The main works of this paper are as follows:1. The excitation energies, oscillator and rotational strengths, as well as the CD spectra for the 16 isomers of tris-diamine ruthenium chelates have been calculated at the B3LYP/LanL2DZ+6-31G* (LanL2DZ for Ru and 6-31G* for other atoms) levels using the TDDFT method including solvent effects. The individual contributions of the chiral arrarys, A/A octahedral core,δ/λtwists of the rings, and the R/S chiral carbons to the circular dichroism spectra of these chelates have been determined and graphically presented. It was found that there is a linear relation between the CD spectra of chelates and the contributions of these chiral arrays. By simply combining the contributions of related chiral arrays in the chelates, all CD spectra of the 16 isomers obtained at the TDDFT level can be well reproduced, and those of the other conformers can also be well predicted, as expected. These findings not only make it possible to determine the absolute configurations and conformations of related chelates in solution from their CD spectra, but also provide a deep insight into the chiroptical properties of the chelates.2. In order to examine the generality of conclusions obtained above, calculations and analyses have also been done for the 16 isomers of tris-diamine cobalt chelates at the B3LYP/6-311+G(2d, p) level. The results showed that the linear relationship between CD spectra of these chelates and the contributions of chiral arrays is also exist in these chelates. Therefore, the intuition-based concept of chiral arrays being responsible for the chiroptical properties of such compounds, have been confirmed in this paper at least for these two kinds of chelates.3. Comparing the transition energies and the chiral parameters△,δand R of related transitions in chelates with different structures and different symmetries, we found that they are also closely related. Therefore, it is possible to get a set of mean parameters and excitation energies to predict all the CD spectra of the three kinds of chelates, including those conformers which have not been treated above. All of these have been done using a program written by ourselves. These results provide a theoretical basis for predicting the absolute configurations of such complexes in solution directly.4. Additionally, the chiroptical properties of tris-acetylacetone chelates of cobalt, rhodium and iridium have also been investigated, with emphasis focusing on the influence of d-p mixture to the exciton spilting and discrimination of absolute configurations. The results showed that the shape of exciton spilting bands in short wavelength region has been changed by the strong d-p mixture so much that cannot be used to determine the absolute configuration. However, the first Cotton effect in the long-wavelength region is still well isolated, and can be used to determine the absolute configuration of such chelates.