Chemistry and Biochemistry
Bayer School of Natural and Environmental Sciences
Dithione, Dithione fold, Metalloenzymes, Model Complexes, Molybdenum, Redox noninnocent
The coordination chemistry of dithiolene complexes has attracted enormous interest by inorganic chemists due to their presence in biological systems and possible applications in material science. Dithiolene units have been identified at the active site of metalloenzymes, containing molybdenum and tungsten. Model complexes have played a significant role in understanding the structural and reactivity of the active site of these enzymes.
In Chapter 2, we report the synthesis of a series of molybdenum complexes, MoIVO(p-SC6H4X)2(R2Dt0), where R = iPr or Me and X = H, Cl, CF3, Me, OMe and tBu, to serve as model complexes for the active site of the molybdenum containing enzymes (molybdenum cofactor). These complexes were characterized by NMR, IR, UV-vis, and electrochemistry. In some cases, where quality single crystals were obtained, they were characterized by X-ray crystallography. Two representative complexes, MoIVO(SC6H5)2(R2Dt0) (R = iPr, and Me) were further investigated for substrate reduction, involving oxygen atom transfer (OAT) from inorganic substrates, namely; trimethyl amine N-oxide (TMAO), dimethyl sulfoxide (DMSO) or nitrate (NO3-). These reactions were followed by UV-vis and NMR spectroscopy. These complexes were capable of reducing TMAO, but not DMSO or NO3-, and were oxidized to corresponding MoVI complexes. In solution, the oxidized complexes (MoVI) were reduced to the parent MoIV center by tertiary phosphines; trimethyl phosphine (PMe3), dimethyl phenyl phosphine (PMe2Ph) and triphenyl phosphine (PPh3), hence completing the catalytic cycle. However, in these reactions, PMe3 and PMe2Ph, coordinates to the parent Mo(IV) complex, hindering the reactions. The corresponding phosphine oxides and coordinated phosphines were detected by 13P NMR spectroscopy.
In Chapters 3 and 4, we explore the coordination chemistry of selected first row transition metals with dithione ligands. We have synthesized a series of iron (Fe), copper (Cu), cobalt (Co) and zinc (Zn) complexes containing 1, 4-diisopropyl-2, 3-piperazinedithione (iPr2Dt0) and 1, 4-dimethyl-2, 3-piperazinedithione (Me2Dt0) dithione ligands. These complexes form the first series of first row transition metals containing dithione ligands to be synthesized. They were also characterized by NMR, IR, UV-vis, and electrochemistry and in some cases X-ray crystallography. Iron and cobalt complexes exhibits octahedral coordination geometry, while copper and zinc exhibit both tetrahedral and square planar geometry.
Mogesa, B. (2014). The Coordination Chemistry of Dithione Ligands: Design, Syntheses, Characterization and reactivity study of Molybdenum and Select First Row Transition Metal Complexes (Doctoral dissertation, Duquesne University). Retrieved from http://ddc.duq.edu/etd/69