Theoretical Studies On The Electronic Structures And Reaction Mechanisms Of Iron Complexes

In recent years, more and more researchers pay attention to the iron complexes because of the abundance, cheapness, favorable biocompatibility of iron. Although experimentalist has made much progress in this area, the electronic structure of some iron complexes and related reaction mechanisms have remained unclear, due to the limitations of existing experimental conditions and means, which affects the development of related reaction systems. Computational chemistry methods are proved to be very effective to solve these complex problems, which would contribute to the development and design of new catalytic system. Herein, the theoretical studies on the electronic structure of four types of iron complexes and their chemical reactions have been investigated by density functional theory (DFT) method.The theoretical study on single-electron reduction of a thiolate-bridged diiron diazene complex regarded as a nitrogenase enzyme mimic indicated that the two-ferrous centers have anti ferromagnetic coupling features. The interaction between diazene ligand and Fe center is a donor-acceptor interaction, showing a major contribution from diazene to metal interaction. The single-electron reduction is a metal-centered process. After the reduction, the acidity of H atom decreases (the frontier electron density of H atom change from 0.003 a.u. to 0.004 a.u.) and the basicity of N atom increases (the frontier electron density of N atom change from 0.058 a.u. to 0.068 a.u.) of the diazene moiety, which are beneficial to proton capture and further ammonia release. An exploration of the electronic structure of nine single-atom bridged binuclear iron phthalocyanines revealed that the phthalocyanine ligand is a good electron "reservoir", and most of these complexes have antiferromagnetic coupling features.The detailed mechanism on alkenylamine intramolecular hydroamination catalyzed by a ?-diketiminate iron complex has also been explored by DFT calculations. The results suggest that the complex has UKS(S= 2) ground state, and the unpaired electrons manily reside on the Fe center. During the generation of active species, the reaction followed Fe-assisted a-bond metathesis (?-BM) mechanism rather than the oxidative addition/reductive elimination (OA/RE) mechanism. During the catalytic cycle, the reaction followed Fe-assisted concerted C-H and C-N bond formation mechanism rather than a stepwise a-bond insertion mechanism. And, this concerted mechanism is found to work for intramolecular hydroamination reaction of the analogous alkenylamine.DFT studies on the. mechanism of regioselective polymerization of 1,3-dienes catalyzed by a bipyridine-ligated iron complex have been performed. During the reaction, the complex has UKS(S= 2) ground state, the unpaired electrons are mainly concentrated on the Fe center and are almost not distributed on the ligand. Therefore, the redox-active bipyridine ancillary ligand in the polymerization reaction is found to be redox-inert. In the insertion transition state, the ancillary ligand is less deformed compared to the remaining part. Compared to the electronic factors, steric effects play a more important role in regioselective polymerization of isoprene.In summary, the current computational studies on iron complexes have been conducted in this thesis, which provide the theoretical information on the design and development of new efficient catalytic systems in the future.