The Study On Reaction Mechanism Of C-O And C-S Coupling Reaction Catalyzed By Copper Halide

The mechanism of CuCl₂-catalyzed chlorocyclization reaction ofethyl（2-methylocta-2,3-dien-4-yl） phosphonate and CuI/BtH catalyzed C-S couplingreaction of benzenethiol and1-bromo-4-methoxybenzene to synthesize（4-methoxyphenyl）（phenyl）sulfane were studied by density functional theory B3LYPmethod. The geometries of the reactants, transition states, intermediates and productswere optimized at the6-31+G（d） level. A vibration analysis and an energy calculationand IRC calculation proved the authenticities of the intermediates and the transitionstates. Atoms in molecules （AIM） and nature bond orbital （NBO） theories were used todiscuss the bond nature and orbital interactions at the same levels. In the firstmechanism, reactant （Re） and catalyst CuCl₂can form the intermediate IM9through theIAand IBtwo possible reaction paths. The activation energies of their limiting steps are129.61kJ·mol^-1and142.10kJ·mol^-1. For the next reaction steps from the intermediateIM9to the product （Pr）, there are two possible reaction paths PAand PB, which limitingstep activation energies are179.55kJ·mol^-1and9.83kJ·mol^-1. Both paths IAâ†'PBandIBâ†'PBmay occur simultaneously. The path IAâ†'PBis the lowest activation energy inthe whole reaction.In the next mechanism, both in the CuI catalyzed reaction and the CuI/BtH catalyzedreaction, multiple reaction pathways have been found by theoretical calculation in thegaseous phase and in DMF solvent. The process in the gas phase is consistent with thatin DMF solvent, but, according to energy analysis, complexes are more stable in DMFsolvent. In the CuI catalyzed reaction, the optimal pathway is PB2. The rate-controllingstep of pathway PB2is IM9â†'TS7â†'IM10and the reaction energy barrier is154.94kJ/mol （sol）； consider the action of alkali KOt-Bu in the mechanism, Therate-controlling step is IM4â†'TS2â†'IM5and the reaction energy barrier is189.58 kJ/mol （sol）.In the CuI/BtH catalyzed reaction, the optimal pathway is IA. Therate-limiting step of pathway IAis M1â†'TS1’â†'M2and the reaction energy barrier is121.58kJ/mol （sol）；consider the action of alkali KOt-Bu in the mechanism, Therate-controlling step is M4â†'TS2’â†'M5and the reaction energy barrier is104.42kJ·mol^-1（sol）. The theoretical calculation results demonstrate that the activation energyof the rate-controlling step and the dissociation energy of the catalyst are reduced withthe introduction of the ligand BtH. Thus, the ligand BtH can promote the reaction andincrease product yield which is in accordance to experimental results. In our research,the proposed reaction mechanism has been explored and a novel coupling reactionpathway has been revealed. The possible cause for CuI catalyst failure on reactionpromotion is the high dissociation energy of CuBr and the high activation energiesalong the reaction pathway. Each transition state needs higher activation energy in theDMF solvent than in the gas phase。...