Synthesis of Non-heme Iron Oxygenase Model Complexes and Their Catalytic Properties

Abstract: The research on non-heme iron oxygenases has emerged as a hot project in bioinorganic field, which has attracted much attention. 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 substrate such as alkanes, alkenes and phenols by using “green” oxidants. It may give a promising way to substitute present oxidation processes. In recent years, the development of biological techniques and biomimetic model systems has led to exciting breakthrough in the field of non-heme iron oxygenases. Encouraged by these achievments, in this thesis, the work focused on mimicking the function of non-heme iron oxygenases, especially those for alkane hydroxylation (iron bleomycin (FeBLM)) and catechol’s intradiol cleavage dioxygenase (protocatechuic 3,4-dioxygenase (3,4-PCD)). A series of iron complexes were synthesized as functional models of non-heme iron oxygenases, their catalytic properties for the hydroxylation of alkanes and activities for the catechol intradiol-cleavage were investigated.A versatile ligand L~1 (N-(2-(pyridylmethoxyethyl)-N,N-bis(2-pyridylmethyl)amine) and its iron complexes were synthesized. The crystal structures of the iron complexes show that that L~1 can act as a tridentate or pentadentate ligand in monoiron complexes and μ-oxo dinuclear iron complex which was obtained from the reaction of L~1 with Fe(ClO_4)_3. Under mild conditions, the catalytic property of complex [FeL~1Cl]PF_6 (Fe2) was explored by using H_2O_2 as oxidant, which exhibited higher chemo-selectivity than previously reported N_5 ligand iron complexes (A/K = 2.4). The result manifests that the weak coordination of ether oxygen atom from L~1 benefits the metal-based oxidation pathway. Complex FeL~1Cl_3 (Fe3) with a fac-configuration showed a high selectivity in alkane hydroxidation as well as Fe2. The activity and selectivity of Fe3 are higher than the N_3-coordinate analogue with a mer-configuration (A/K = 2.3). While in mCPBA system, the complexes bearing N4O and N_2O_2 ligands exhibited high activities and high regioselectivities (3°/2° = 18.5-34.4). An Fe~(III)-OOH species was detected when the cyclohexane oxidation catalyzed by [FeL~2](ClO_4)_2 (Fe6, L~2 =N,N-bis(2-pyridylmethoxyethyl)-N-(2-pyridylmethyl)amine) containg an N_2O_2 ligand was monitored by UV-Vis spectrometry.The μ-alkoxo diiron(III,III) complex [FeL~8(NO_3)]_2(NO_3)~2 (Fe11, HL~8 = N,N-bis(2-pyridylmethyl)-N-hydroxylethylamine) containing tripodal N_3O ligand wa…
Key words: Non-heme iron oxygenases; Iron complexes; Bioinorganic chemistry; Alkane hydroxyltion; Catechol intradiol-cleavage; Crystal structure; Unsymmetric linear N_2O_2 ligand; Tripodal N_3O ligand

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