Theoretical Study On The Formation Mechanisms Of Carbon- Carbon Bonds Catalyzed By Copper Or Nickel Catalysts

Density functional theory (DFT) calculations were performed to investigate the mechanisms of organic reactions catalyzed by copper or nickel compounds, where the formation of carbon-carbon bond play an important role in the atoms transformation process. The reactions consists of the following chemical processes, pyrrole synthesis switched by copper and nickel catalysts, the skeletal rearrangements of O-propargylic oximes catalyzed by cuprous, and trifluoromethylation of iodobenzene with copper trifluoromethyl complexes. The results from the DFT calculations are agreement with experimental reports, which contribute to understand the reaction deeply and design synthetic methods efficiently.1. Pyrrole synthesis switched by copper and nickel catalystsThe reasons of regioselectivity of 2,4-or 3,4-disubsituted pyrrole switched by cupric acetate and nickel chloride have been explored in detail by DFT method. The (1-azidovinyl)benzene and 2-phenylacetaldehyde are regarded as model reactants. In these reactions, two activity intermediates of 3-phenyl-2H-azirine and 2-phenylethen-1-ol are formated from two reagents respectively, the intermediates are bonded with a carbon-carbon bond, and the following step is cyclized with a carbon-nitrogen bond. The postions of substituents are fixed after cyclization, so it is adequate to calculate the cyclization process.The results from DFT calculation indicated that the selection of the two catalysts are originated form the different positions of nucleophilic reaction between azirine and enol. The carbanion of enol is favorable to attack the saturated carbon atom of azirine which lead to 2,4-disubsituted product under the cupric acetate catalytic condition. On the contrary, if the catalysts is the nickel chloride, the carbanion is tend to attack the unsaturated carbon which results in the formation of 3,4-disubsituted pyrrole.2. The skeletal rearrangements of O-propargylic oximes catalyzed by cuprousA variety of rearrangements of O-propargyl oximes caused by different catalysts producing the corresponding products, including four-membered ring compounds which are difficult in synthesis. From the experimental reports, both of catalysts and substituent groups have important influence on the rearrangement process. In order to study this process systematically, CuOAc, CuCl, CuBr, and Cul are selected as catalysts for rearrangement process of eight substrates substituted with different substituent groups.We propose three rearrangement mechanisms. Path A, the reaction is starting with the N-terminal of oxime attacks to alkynl activated by coordinated of catalysts initially, the carbon-oxygen bond is broken then carbon-carbon bond could be formed. Path B, the reaction began with a concerted transition state after the catalysts coordinated the oxygen, in this transition state the carbon-oxygen bond breaking was almost simultaneous with carbon-nitrogen bond formating, and then the carbon-carbon bond is forming. Path C, the reaction started with C-terminal of oxime attacks alkynyl activated by coordinated of catalysts, carbon-nitrogen bond forming after the carbon-oxygen bond breaking.3. Trifluoromethylation of iodobenzene with copper trifluoromethyl complexesThe Density Functional Theory (DFT) calculations were performed to investigate the reaction mechanisms between well-defined NHC copper trifluoromethyl and iodobenzene. Two possible reaction types are proposed, the coupling reaction of NHCCuCF3 with PhI, and single electron transfer (SET). Four reaction routes have been computed to account for the coupling reaction type, involving the generation of difluorocarbene, proceeding via oxidative addition-reductive elimination (OARE), iodine atom transfer, and σ-bond metathesis, respectively. As for the SET type, two possible ways distinguished by electron donors have been computed. Both of two type mechanisms have the same rate-determining step of breaking of Py-I bond, however, the intermediates are unfavourable in energy relative to the reagents, and carbon-carbon bond formation between trifluoromethyl and phenyl is the critical step to obtain the product.