Conformational Analysis and Absolute Configuration Determination of Some Organic and Coordination Chemistry Compounds Using Chiroptical Spectroscopy and DFT calculations

• Author / Creator

  Dezhahang, Zahra

• My PhD thesis projects revolve around three main parts, namely synthesis, conformational analysis, and absolute configuration determination of a number of chiral Schiff base ligands and axial chiral binaphthyl type ligands or molecules and some of their transition metal complexes in solution. To obtain the structural information of these chiral systems in solution, chiroptical spectroscopic techniques, such as electronic and vibrational circular dichroism (ECD and VCD) spectroscopy, as well as the related linear spectroscopy, i.e., IR and UV-Vis spectroscopy, have been used as the main experimental tools. In addition, density functional theory (DFT) has been employed to perform all calculations for the conformational searches, geometry optimizations, and simulations of VA, VCD, UV-Vis, and ECD spectra. Comparison of the theoretical and experimental spectra has been utilized to provide detailed and rigorous spectral interpretations and therefore to extract essential structural properties of the targeted species in solution. To account for the bulk solvent environment, the implicit solvation approach, i.e. the polarizable continuum model (PCM), has been applied where no strong solvent–solute hydrogen-bonding interactions are expected. Initial conformational analyses of the systems studied have been performed using small basis sets, such as 6-31G(d). For the final calculations, several larger basis sets, namely 6-31++G(d,p), 6-311++G(d,p), and cc-pVTZ have been used for the C, H, N, O atoms and the LanL2DZ basis sets for the metal atoms. We found that flexible ligands, such as the multidentate nitrogen donor ligands, BINAP and related ligands, show a number of minima on their potential energy surfaces. Further coordination to one or more metal centers often introduces dramatically the structural rigidity and consequently results in a smaller number of minima. For example, in the case of Pd(BINAP)Cl2 and Pd(TOLBINAP)Cl2, a single conformation has been identified in solution. Especially for the VCD spectra observed, it has been demonstrated that the gas phase models failed to capture the experimental optical responses properly, and the inclusion of solvent whether implicitly or explicitly has been shown to be of high importance. In addition, in the study of a triply axial chiral binaphthyl based molecule, it has been demonstrated that the solute concentration may play a crucial role on its conformational landscape as well as its axial chirality in solution. To probe structural properties including induced chirality at the metal centers, the bis(pyrrol-2-ylmethyleneamine)-cyclohexane (H2L) ligand and its five metal complexes (e.g. Ni (II), Cu (II), Pd (II), Pt (II), and Zn (II)) have been synthesized and their VA, VCD, UV-Vis and ECD spectra have been recorded and analyzed. We found that while M-Ni-(R,R)-L, M-Cu-(R,R)-L, M-Pd-(R,R)-L, and M-Pt-(R,R)-L complexes take on the mono-nuclear geometries, the [M-Zn-(R,R)-L]2 complex in solution exists in the dinuclear geometry. Furthermore, these metal complexes take on M-helicity as dictated by the chirality of the (R,R)-ligand.

• Subjects / Keywords

  • Absolute Configuration
  • Conformational Analysis
  • DFT calculations
  • Chiroptical Spectroscopy

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3RX93M0Q

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.