Synthesis And Performance Study For Chemical Simulated Complexes Of [FeFe]-and [Fe]-Hydrogenase Active Sites

Hydrogenase is a metal enzyme that exists in anaerobic microorganisms in the nature.It can catalyze the proton reduction as well as its reversible chemical reaction which is the hydrogen oxidation.The biomimetic simulation of its active site is a significant work in the field of chemistry and chemical engineering for its broad application prospects.In this work,the structures of[Fe Fe]-hydrogenase and[Fe]-hydrogenase active sites were used as templates,the corresponding synthetic conditions to the different complexes were explored by selecting suitable ligands;the model complexes closed to the structural characteristics of the natural hydrogenase active site were synthesized;the relationships between the structures of the model complexes and their catalytic proton reduction performances were studied;the mechanisms of model complexes during catalytic process were explored;the expanded applications of the model complexes of Fe-containing hydrogenase were further studied.The[Fe]-hydrogenase model complex was used as the catalyst in the reaction of hydroxylation of phenol to dihydroxybenzene(DHB)and its catalytic performances were studied systematically.This work was summarized as follows:1)Complex 1,[?-(SCH(CH₂CH₃)CH₂S)-Fe₂(CO)₅]₂-(?¹-DPPE)and complex 2,[?-(SCH(CH₂CH₃)CH₂S)]Fe₂(CO)₅(?¹-DPPM),were synthesized and characterized.Even though 1 and 2 shared the similar electron and space environments around metal center,1 with two symmetrical[2Fe2S]groups featured four reduction peaks in CV,and it was more sensitive to the amount of acid.It was suggested that two[2Fe2S]groups in 1 played different roles in the process of proton reduction.One[2Fe2S]group could be regarded as the[4Fe4S]moiety with adjustable valence.2)Fe₂(CO)₃[?-(SCH(CH₂CH₃)CH₂S)](?-DPPM)(?¹-DPPM)(3)was designed,synthesized and characterized.As a natural[Fe Fe]-hydrogenase model complex,3 not only overcame the steric hindrance,met the requirements of structure with 3×CO and3 substituents,but also showed closed features to the natural[Fe Fe]-hydrogenase active site in oxidation potential and the infrared spectrum.3 can show a better proton reduction performance compared with 2,indicating that the?-DPPM can served as a more efficient shuttle for proton and electron.3)?-(SCH(CH₂CH₃)CH₂S)-Fe₂(CO)₄(?²-DPPE)(4)was synthesized and characterized.Different electrochemical characteristics and infrared spectrum under different atmospheres(nitrogen and carbon monoxide)in 4 indicated its isomerization with various conditions.The proton reduction performance of 4 in CH₃CN/H₂O(50:1,v/v)showed the best catalytic efficiency;the reaction system with the solvent of CH₃CN in the presence of H₂O under nitrogen atmosphere and the reaction system with a neat CH₃CN solvent under carbon monoxide atmosphere would trigger the same isomerization effect in 4.4)A six-coordinated iron complex Fe^?(CO)₃I₃-[trimethylpyridine-H](5)was synthesized at room temperature,which could be used as a catalyst in the hydroxylation reaction of phenol to DHB under a mild condition.The catalytic reaction could be carried out smoothly at ambient temperature using low concentration H₂O₂(30%wt.)as an oxidant.The phenol conversion rate was 20.5%,the DHB selectivity was 86.5%with a ratio 2.9 of CAT/HQ.5)As a precursor of[Fe]-hydrogenase,Fe I₂(CO)₃PPh₃(6)was used as a catalyst for the hydroxylation of phenol to DHB.H₂O₂was used as the oxidant in the reaction.Under ambient temperature in aqueous solution,the conversion rate of phenol was26.7%,the selectivity of DHB was 80.0%,and the molar ratio of CAT/HQ was 2.1.The catalytic reaction mechanism was corresponded to the hydroxyl radical mechanism.The kinetic studies indicated that the reaction was an apparent secondary reaction.The apparent activation energy Ea was 66.36 k J/mol,and the pre-exponential factor A was 8.91·10⁵m³/mol·S.