Synthesis And Characterization Of Transition Metal Complexes With Tris(2-Pyridylmethyl)Amine Derivatives

The tripodal ligand TPA (Tris(2-pyridylmethyl)amine) and its derivatives play an important role in mimicing metalloproteins with Fe, Cu, Mn centers which are versatile ligands to form stable complexes with a large number of transition metals. Metal complexes of Fe, Mn and Ru with TPA ligand have carried out catalytic oxidation of hydrocarbon. However, most information has been concentrated on parent TPA complexes and the information of substituted TPA have been reported very little at present. It is lack of research on how the ligand environments affect the function of their complexes. Therefore, it is important to synthesize more substituted TPA derivatives, systematically study their complexes, establish the correlation between the structure and reactivity of complexes.A series of TPA derivatives were synthesized which were substituted in the α or β position of one pyridyl arm with different electronegative and size groups, especially two TPA derivatives substituted with aminomethyl groups in the a position of one or two pyridyl arms were obtained. Introduction of aminomethyl groups can reduce redox potentials of complexes and provide the possibility to fix dioxygen and anchor water though hydrogen bond of aminomethyl groups.Effects resulting from substituted properties of ligand on the spectroscopic, electrochemical, structural properties of the robust chloroferric complexes have been investigated. It was found that the steric hindrance provided by the α-substituted arm pushed it away from the coordination and the mononuclear chloroferric complexes were coordinated by three nitrogen atoms of unsubstituted pyridine and three chloride atoms, forming a distorted octahedral geometry. The mononuclear chloroferric complexes bearing one OH substitute in the β position of one pyridyl arm of TPA ligand were coordinated by three nitrogen atoms, one oxygen atom of TPA ligand and two chloride atoms, leaving one nitrogen of pyridine free and potentially reactive and their absorption maximum were red-shifted, about 112 -174 nm compared with that of parent [TPAFeⅢCl3] complex. Electrochemical analysis showed that substituted NH2CH2 and OH groups reduce the redox potentials of FeⅢ/FeⅡ, which make to stabilize higher oxidation state.The crystal structure of two (μ-oxo)diiron(III) complexes of pentadentate TPA substituted by one hydroxymethyl in the a position of one pyridyl arm were obtained. The Fe-O-Fe bond angle of two complexes were distinct, especially the effects of the Fe-O-Fe angle of two complexes on electronic spectra were reverse from that of other reported (μ-oxo)(TPA)2Fe2Ⅲ,Ⅲ complexes.In order, to mimic the structure of oxygen evolving center (OEC) in donor side of natural photosystem II, three (μ-oxo)2Mn2Ⅲ,Ⅳ complexes were designed and synthesized. The crystal structures showed that Mn-Mn distance was 0.26 nm which was close toMn-Mn distance of OEC(0.27-0.28 nm). The cyclic voltammeters studies showed that increase in potential was attributed to the electron-donating group of TPA ligand and the reduce in potential resulted from electron-withdrawing group of TPA ligand. Four kinds of ruthenium complexes of TPA were synthesized by modified preparation method and one TPARuⅡ crystal coordinated by the solvent acetonitrile was characterized.Five kinds of binuclear Ru-Mn complexes with different Ru-Mn distances have been synthesized and characterized. With the Ru-Mn complexes, it was demonstrated that electron transfer occurred from MnⅡ to RuⅢ upon photo-oxidation of the RuⅡ complex in the presence of methylviologen. The rates of electron transfer from MnⅡ to RuⅢ ranged from 2.5 × 104s-1 to 7.1 × 104 s-1. The results indicated that the Ru-Mn distances affected the rates of intramolecular electron transfer from MnⅡ to RuⅢ which provide the important information to design photoinduced oxidation reaction by using solar energy.