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In biological systems, O2 interaction with iron centers in enzyme structure occurs during respiration and the metabolic process. To fully understand the interaction mechanism, each step of the O2 reduction process is important and needs to be characterized. To this goal, we have synthesized and characterized a series of cationic five-coordinate iron complexes, [FeII(L)(L')]+ where L is TpMe, Me = hydrotris{3,5-dimethylpyrazol-1-yl}borate; TpPh, Me = hydrotris{3-phenyl-5-methylpyrazol-1-yl}borate; L'= 2,2'-bipyridine; 4,4'-dimethoxy-2,2'-bipyridine; 4,4'-dimethyl-2,2'-bipyridine; 4,4′-bis(trifluoromethyl)-2,2′-bipyridine; 4,4'-dibromo-2,2'-bipyridine. These complexes were utilized to activate O2 to isolate iron-oxygen intermediate species. The electronic spectra indicate intense absorption at 390 nm consisting of O2 binding to the mononuclear iron complex that generates an iron oxygen intermediate. In addition, the effect of the ligand on the stability of the potential intermediate was studied by altering the ligand substitute. We also treated the high-spin iron(II) reaction with CO to generate the corresponding adduct of low-spin iron(II). 1HNMR analysis reveals a diamagnetic complex arising from a spin-state change from S = 2 to S = 0. Furthermore, infrared spectroscopy has been used to support CO binding empirically. In chapter 3, my research studies nitrene chemistry. Nitrenes are chemically analogous to a single oxygen atom (i.e., NR vs. O). Therefore, nitrene can insert into other chemical bonds. Such reactivity can install synthetically valuable carbon-nitrogen bonds into hydrocarbon substrate. Affording shorter routes to high-value commodity chemicals. However, free nitrenes are generated with difficulty and often display rapid and unselective reactivity. Some degree of control can be achieved through the coordination of nitrene within the ligand field of a metal complex. Structural and electronic modifications affect nitrene reactivity and enable catalyst optimization by characterizing reactive intermediates. We provided a rare example of an octahedral high valent iron imido complex. In chapter 4, polydentate ligand systems have been used to synthesize a new series of late first-row transition metal complexes. We employed Tp hydrotris(pyrazolyl)borates and Bp hydrobis(pyrazolyl)borates to synthesize five-coordinate complexes, [(L)M(L')] where (L is TpPh, Me, TpMe, Me; L'= BpPh, Me, BpH, H; and M= Fe, Co, Ni) to investigate their coordination chemistry. Various sterically hindered ligand systems show an interesting effect on the ligand orientation in the complex structure. |
