Studies On The Catalytic Activities Of New Olefin Metathesis Catalysts And Reaction Mechanisms On Nucleophilic Aromatic Substitution Reactions

The investigation of mechanisms for the metathesis reaction catalyzed by a new catalyst we designed and the base-promoted aromatic nucleophilic substitution were carried out with the aid of density functional theory(DFT) method. The main contents of this paper are:1. In the first part of this paper, the detailed mechanisms for the metathesis reaction catalyzed by a new catalyst we designed were studied. All of the transition states and intermediates were performed with the M06 method. Vibration analysis and intrinsic reaction coordinates(IRC) were calculated for the transition states to confirm that such structures indeed connect two relevant minima. According to the widely accepted Chauvin mechanism, the computational data gives a possible route as followings. The mechanism includes three separate parts: ligand exchange, cycloaddition and [2+2] cycloreversion. The rate-determining step is in the ligand exchange progress with energy barrier of 22.7 kcal/mol. The Grubbs 2nd generation catalysts were also investigated at the same level in order to prove the catalytic ability of the new catalyst by a comparison. Theoretical investigations suggest that the new catalysts is easier to dissociate a tertiary phosphine PR3(R = Ph, Cy, etc) ligand, which might match the requirements of a good performing olefin metathesis catalyst.2. The mechanism of the base-promoted aromatic nucleophilic substitution were examined. All of the transition states and intermediates were performed with the M06 method. Three possible reaction positions which related to the formation of para, meta and ortho products are investigated in three possible reaction modes: direct attack, carbanion attack and attack with the presence of tetrahydrofuran(model 1-3). Computational results suggest that the reaction is more likely to occur at the electron deficiency orth and para position of octafluorotoluene due to the electric effect of CF3 group. And the carbanion and fluorine ion could astrict electron strongly. There is certain repulsion between the attack group and the leaving group. Comparison of the density functional results with those from the three models shows that para-substituted product is formed as the energetically favored product in model 3 which agree with the experimental results.