Reactivity Of Uranium Complexes And Construction Of Uranium-Transition Metal Multiple Bonds

The study of bonding and reactivity of actinides is of key importance for the understanding the nature of the bonding of the f elements.Uranium is one of the most intensely researched actinide elements.Since the beginning of the 21 st century,a series of non-aqueous uranium complexes have shown unique properties in catalysis,small-molecule activation,and single-molecule magnets.It is well known that ligands are essential to the development of organometallic chemistry.The electronic structures and reactivities of uranium complexes formed by different ligands are quite unique.In this thesis,a series of novel uranium complexes were synthesized and their reactivities were also studied by using a novel triamidoamine N-P ligand.The main research contents of each chapter are as follows:Chapter 1 briefly introduces: 1)synthesis and small-molecule activation by low-valent uranium complexes;2)synthesis and reactivity of uranium-nitride complexes with different oxidation states;3)construction and reactivity of uranium-metal bonds,mainly describing the development of uranium-metal bond chemistry,the types and construction strategies of uranium-metal bonds.In the end,the research objectives and purposes of this dissertation are presented.Chapter 2 describes a facile dinitrogen and dioxygen cleavage by a uranium(III)complex via the cooperativity between the non-innocent ligand and the uranium center.A uranium(III)dimer was successfully isolated by the reduction of a uranium(IV)complex with KC8 in the presence of TMEDA under argon.This complex can achieve a six-electron reduction of N2 under ambient conditions taking advantage of the synergistic effects between U(III)and P(III).The reduction product could be hydrolyzed to an N-containing organic compound or ammonia with different equivalents of water.The U(III)-P(III)synergism can also achieve an eight-electron reduction of two molecules O2.All these complexes were fully characterized and the mechanisms for the N2 and O2 cleavage were studied by DFT calculations.Chapter 3 deals with synthesis and characterization of uranium(IV and V)nitride complexes.Uranium azide was synthesized by salt elimination of N[CH2CH2NPiPr2]3UCl and Na N3.X-ray diffraction shows that the uranium azide complex is a dimer,bridged by two azide groups.Under heating or UV light,the N2-activated product shown in Chapter 2 was obtained.When reduced this uranium azide complex with different alkali metals,produces a series of novel uranium nitride complexes.These complexes were characterized by elemental analysis,single crystal X-ray diffraction,NMR spectroscopy,SQUID,and absorption spectroscopy.Chapter 4 describes heterometallic molecular clusters featuring triple bonds between uranium and transition metals.The species containing uranium-iron triple bonds or uranium-cobalt triple bonds were synthesized by the reduction of a mixture of [N[CH2CH2NPiPr2]3UCl] and Fe Cl2 or Co Cl2 with 4 equivalents of KC8.The bond lengths of the uranium-iron and uranium-cobalt are about 1.96 and 2.09 (?),respectively.The complex {N[CH2CH2NPiPr2]3UFe Cl}2 can be further reduced by 2equivalents of KC8.These complexes represent the first structurally authenticated examples of multiple bonding between f-block elements and first-row transition metals.These complexes were fully characterized and the electronic structure of the uranium-metal triple bond were analyzed by quantum chemical DFT calculations.Chapter 5 presents a brief summary of this dissertation and the prospect of the future research.