DFT Studies On The Mechanisms Of The Stille Reaction And The Dearomatization Reaction Catalyzed By Palladium

The reaction mechanisms of the Stille reaction and the dearomatization reaction catalyzed by Palladium have been analyzed by means of DFT methods for the coupling of benzyl chloride with allyltrimethylstannane. Theoretical calculation has been carried out at the B3LYP level. First, the calculations indicate that the dearomatization mechanism is energetically favorable and the overall energy barrier of this mechanism is 18.91 Kcal/mol. It is insurmountable in energy for the Stille reaction mechanism. The overall energy barrier of cyclic mechanism and open mechanism is 34.82 Kcal/mol, above 100Kcal/mol, respectively. Secondly, the effect of solvent has been also considered for all mechanisms. The solvent acetone, THF, water, carbon tetrachloride are chosed. The calculation results show that the energy barriers for the dearomatization reaction path and the Stille cyclic reaction path are insignificantly changed while the overall energy barrier decreases obviously for the Stille open reaction path, especially for the step of substitution of the chloride ligand by a PH3 ligand to generate a cationic species, from 109.54 Kcal/mol decreases to 1.84 Kcal/mol. Thirdly, The influence of the ligand has been also studied, and it was found that the reaction mechanism can be modulated from dearomatization to Stille by exchange of PdL2 ligand, the overall energy barrier of Stille mechanism has been decreased from 34.82 Kcal/mol to 22.51 Kcal/mol. Further, the method of natural bond orbital(NBO) has been perfomed to investigate the changes in electron density redistribution leading to reaction changes and product formation. NBO analysis demonstrates that a superior Pd-allyl geometry is important in dearomatization mechanism.