Phenolate Derivatives of Octanuclear Iron-Oxo-Pyrazolato Complexes; Enantiomeric Resolution of T-Symmetry Species

Authors

Konstantinos Lazarou, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Chemistry

First Advisor's Name

Raphael G. Raptis

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Konstantinos Kavallieratos

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Kathleen Rein

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

David Chatfield

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Daniela Radu

Fifth Advisor's Committee Title

Committee member

Keywords

Polynuclear complex, Iron-oxide, Chirality, Chiral resolution, X-ray crystallography, Mössbauer spectroscopy, Electrochemistry, Circular dichroism, Paramagnetic NMR, Synthesis, Characterization, Pyrazole, Phenolate

Date of Defense

5-14-2019

Abstract

Octanuclear ferric complexes involving achiral phenolates of the general formula [Fe₈(μ-O)₄(μ-pz)₁₂(R-C₆H₄O)₄], (R = 4-NO₂, 4-CN, 4-F, 4-Cl, 4-I, 4-CH₃O, and 3-NO₃), where synthesized and characterized by single crystal X-ray crystallography, elemental analysis, ¹H-NMR, UV-Vis, IR, ⁵⁷Fe Mössbauer spectroscopy and electrochemical methods (cyclic and differential pulse voltammetry). Results indicate that the nature of the phenolate substituents allows the fine tuning of the spectroscopic data of the compounds.

Subsequently, this project focused on the resolution of the racemic octanuclear iron-oxo-pyrazolato complex [Fe^III₈(μ-O)₄(μ-4-R-pz)₁₂Cl₄], [Fe₈], (R=H, Me, Cl) to its P and M enantiomers. The strategy employed towards that goal was the diastereomer formation via substitution of the terminal chloride ligands with the chiral (R, S) 4-sec-butylphenol. Substitution with rac-4-sec-butylphenol reveals selectivity of the Fe₈ P and M enantiomers for the phenolate R and S enantiomers, respectively. In the case of the 4-H-pz and 4-CH₃-pz derivatives, this selectivity is manifested in their X-ray structures and ¹H-NMR spectra. However it does not result in resolution, as the enantiomers cocrystallize as racemates. In contrast, the 4-Cl-pz derivative crystallized in non-centrosymmetric (chiral) space group, as determined by single crystal X-ray structure determination. The enantiomeric relationship of the P/R and M/S species was further established by Circular Dichroism experiments. These enantiomers are stable towards racemization. Re-introduction of the terminal chloride ligands was achieved via reaction of the P/R and M/S with HCl and the Circular Dichroism spectra of the products showed the presence of the P and M enantiomers in solution with their absolute configuration persisting.

The selective coordination of the R and S phenolates to the P and M complexes constitutes an unprecedented example of enantiomeric recognition in a non-biological system resulting in spontaneous resolution upon crystallization by employing only racemic reagents and media.

Identifier

FIDC007713

ORCID

ORCID ID: https://orcid.org/0000-0003-4917-8080

Recommended Citation

Lazarou, Konstantinos, "Phenolate Derivatives of Octanuclear Iron-Oxo-Pyrazolato Complexes; Enantiomeric Resolution of T-Symmetry Species" (2019). FIU Electronic Theses and Dissertations. 4272.
https://digitalcommons.fiu.edu/etd/4272