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

Konstantinos Lazarou, Florida International University


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 [FeIII8(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.

Subject Area

Chemistry|Inorganic chemistry

Recommended Citation

Lazarou, Konstantinos, "Phenolate Derivatives of Octanuclear Iron-Oxo-Pyrazolato Complexes; Enantiomeric Resolusion of T-Symmetry Species" (2019). ProQuest ETD Collection for FIU. AAI28315901.