DFT Study On Synthesis Mechanisms Of Haloallenes And Structures Of Endohedral Metallofullerenes

In recent decades, the development and application of Density Functional Theory method (DFT) has been greatly promoted by the fast development of computer technology. DFT has been widely applied to investigate various aspects of the chemical reaction mechanisms and the structure of matters. In this thesis, we firstly reviewed the latest developments and applications of DFT and then focused on the formation mechanism of haloallene and structure of metallofullerene.Haloallenes are important chemical intermediates and widely used in organic synthesis. The mechanism of the reaction of propargyl alcohols with N-halogenated succinimide (NXS)/triphenylphosphine(PPh3) to synthesis haloallenes was investigated by DFT based calculations. The overall reaction can be rationalized as the following four-step mechanism: the NXS will first react with PPh3to produce phosphonium salt as the halodeoxosubstitutation catalyst; the phosphonium salt will then react with propargyl alcohol to generate halogenation intermediate; after that, the halogenation intermediate will undergo intramolecular halodeoxosubstitution to form propargyl halides and haloallenes; and the formed propargyl halide will finally isomerize to haloallenes. We found that the halodeoxosubstitutation of propargyl alcohol with NXS/PPh3is a radical reaction with a waterfall-like potential energy surface and does not have contribution to the selectivity of the reaction. In contrast, the isomerization from propargyl halide to haloallene accounts for the product selectivity. We also systematically studied the impact of solvent on the isomerization reaction and found that the isomerization barrier varies inverse propotionally with the dielectric constant of the solvent, which indicates the possibility of control the selectivity by optimization of the dielectric property of the solvent. These findings not only bring insights on the reaction mechanism for the NXS/PPh3catalyzed halogenation of propargyl alcohols, but also provide guidelines for optimized reaction strategies for synthesis of haloallenes.Metals and their hybrid clusters can be encaged into fullerenes to form endohedral metallofullerenes (EMFs). We studied the detailed structure and electronic structure of actinide metallofullerene U@C82via DFT based calculations. We found that#5C82and#8C82are respectively the best cages for the encapsulation of monovalent and tetravalent U cations(i.e., U+and U4+), while#8C82is the best cage for divalent, trivalent, pentavalent and hexavalent U cations(i.e., U2+, U3+, U5+and U6+). Among the isomers investigated, U@#9C82corresponds to the thermodynamically most stable one and thus corresponds to experimentally isolable isomer of U@C82-The calculated spin charges explicitly support that U@#9C82is a trivalent EMF with an electronic configuration of U3+@C823-The predicted structure and electronic properties of U3+@#9C823-are in good agreement with the experimental observations. Therefore, the calculation scheme used here can also be applied to study the electronic structures of other actinide metallofullerenes in the future.