Synthesis And Catalytic Properties Of Iron And Ruthenium Complexes Containing Imidazole Units And Study On Proton Coupled Electron Transfer

In the past decade, the research on non-heme iron oxygenases has emerged as a hot project in bioinorganic field. Several crystal structures of non-heme iron oxygenases were determined with the development of biology techniques, various spectroscopic techniques and crystallography. Crystal structure revealed that imidazole in histidine coordinates to the non-heme oxygenase active site in all proteins, which shows the ligands containing imidazole unit are important in non-heme iron oxygenases. Many non-ringed N₄ ligands were used in functional synthetic models, especially the ligands containing a pyridine moiety. Under mild conditions, the bio-inspired catalysts based on non-heme iron oxygenases can selectively and efficiently catalyze oxidation reactions of a large range of substrates such as alkanes, alkenes and phenols by using "green" oxidants. It may give a promising way to substitute present oxidation processes.Encouraged by these achievments, in this thesis, the work is focused on mimicking the structre of non-heme iron oxygenases using the N₄ ligands with benzimidazole unit. A series of iron complexes were synthesized as functional models of non-heme iron oxygenases, their catalytic properties for the oxidation of hydrocarbons were investigated. Crystal structures showed that all iron centers contain a distorted octahedral coordination gemometry. Catalytic results indicated that the activity of model complexes was lower than the iron complexes containing TPA (TPA = tris(2-pyridylmethyl)amine) . Fe4a exhibited high activities(83.8%) and high regioselectivities(3°/2°= 19.9). The model complex structures are close to the active site of natural enzymes, but catalytic results were not satisfactory.Proton coupled electron transfer (PCET) reaction was also investigated using the model complexes Ru4a and Ru4b, and a proton coupled electron transfer model was created. The NH group of the ligand L⁴ readily undergoes a reversible protonation/deprotonation process, which is confirmed by spectroscopic and electrochemical evidences. The reversible protonation/deprotonation regulates the oxidation potential of the Ru^â…¡/Ru^â…¢redox couple in the range of 430 mV without changing the framework of the ruthenium complex. The kinetics of the PCET was also investigated by spectroelectrochemistry and flash photolysis spectrophotometer, but Ru4a quenched the exited state of Ru(BPY)₃(PF₆)₂.