Theoretical Studies On Olefin Hydrogenation And Cyclic Ester Polymerization Catalyzed By Organo-Iron Complexes

Organo-iron complexes are widely used in various catalytic reactions due to its low toxicity, high terrestrial abundance, and other significant advantages. It has showed excellent catalytic activity in olefin hydrogenation and cyclic ester polymerization. Redox non-innocent ligands can be involved in the elementary bond activation steps in a catalytic cycle. Redox switchable catalysts used in the ring-opening polymerization of cyclic esters are capable of controlling the molecular weight and microstructure of the resulting polymer. In this thesis, the mechanism of olefin hydrogenation catalyzed by bis(imino)pyridine iron complexes- and the ring-opening polymerization of lactide and ?-caprolactone catalyzed by bis(pyrazolo)pyridine iron complexes are investigated through the density functional theory (DFT). The main results are as follows:1. The computational results suggest that the ground state of the bis(imino)pyridine iron complex (iPrPDI)Fe(N2)2 (iPrPDI= ((2,6-CHMe2)2C6H3N=CMe)2C5H3N) is open-shell triplet state and the active species (iPrPDI)Fe(C4H8) has broken-symmetry BS(4,2) (S=1) ground state. Although the bis(imino)pyridine ligand has redox non-innocent feature, the reaction is predicted to occur at the iron center rather than both iron and redox-active PDI ligand. The insertion of olefin adopts 1,2-insertion manner. It is noteworthy that the bis(imino)pyridine ligand and Fe center in the rate-determining transition state possess antiferromagnetic coupling characteristic, which could play an important role in achieving the hydrogenation reaction.2. The ring-opening polymerization of rac-lactide catalyzed by the neutral iron(?) complex is significantly favorable than that catalyzed by the cationic iron(?) complexes. The iron(?)-featured catalytically active species and intermediates involved in the most favorable pathway were demonstrated to have antiferromagnetic coupling characteristic, which correlates to its higher catalytic activity. In ring-opening transition states involved in both iron(?)-and iron(?)-catalyzed reaction pathways, the significant difference of the second-order stabilization energy of the forming Fe-O bond (Fe(?)> Fe(?)) could account for the different catalytic activity of the two catalysts.3. The ring-opening polymerization of ?-caprolactone catalyzed by a bipyrazolylpyridine iron complex has been investigated. The catalytically active species is proposed to be monovalent cation iron(?) species with two alkoxide group. The pathway catalyzed by monovalent cation iron(?) species is more favorable than that catalyzed by the corresponding iron(?) complex. The differences of second-order stabilization energy of C-O bond in nucleophilic addition step between the two pathways (Fe(?)> Fe(?)) further reflected the catalytic activity of the two catalytic systems.