| The traditional organic reactions have often the limited reaction substrates,pre-activation,difficulty in control,high cost and long time.To overcome these limitations,the catalyst came into being.Transition metal catalyzed organic reactions have the advantages of mild reaction conditions,fast rate,high selectivity,atomic economy and so on.The acceleration of the industrial development process requires people to understand the reaction mechanism of transition metal-catalyzed organic reactions at the molecular level,which leads to the application of quantum computational chemistry.Through calculations,people can understand the reaction mechanism better and predict the experiment.Both experiments and computations complement each other.The three chapters of this paper from chapter 3 to chapter 5 select those reactions reported in the experiment,and the quantum chemical method was used to calculate and analyze the reaction mechanism at the molecular level to provide further understanding for such reactions and guidance for designing novel relevant reactions.This study was briefly described as follows:（1）The reaction mechanism of the ruthenium-catalyzed reaction of oxime ether with cyclopropanol was studied theoretically by density functional theory.The mechanism proposed by the experiment authors is that the oxime ether forms a metal-carbon bond through the inner-sphere CMD mechanism,and then the product is obtained by cyclopropanol ring opening,β-H elimination,olefin insertion,and C-H reduction.Prior ring opening is found to be favored over the prior C-H activation,and the outer-sphere CMD mechanism in C-H bond activation is energetically favored.This is because cyclopropanol has a large ring strain,and the first ring opening can release the ring strain,obtaining thermodynamically favorable intermediates.When the inner-sphere CMD mechanism occurs,the molecular structure has reached a stable state of18e,the directing group is unable to coordinate with the metal and a stable intermediate cannot be obtained,making the reaction kinetically unfavorable.（2）The second system of the thesis uses density functional theory to study the reaction mechanism of ruthenium catalyzed allyl amidation.Through research,we found that the favorable mechanism is that under the action of the cationic catalyst,the 1-octene C-H activation occurs first,followed by the extrusion of CO2 to form allyl-Ir-nitrenoid species,the amidation product then obtained after C-N reduction elimination and protonation.The rate-determining step of this reaction is C-H activation,and the selective-determining step is C-N reduction elimination process.Through computational analysis reveals the effects of substituents and transition metals on branch/linear selectivity and the roots of chemoselectivity.（3）The third system of the thesis uses density functional theory to study the reaction mechanism of palladium-catalyzed weakly coordinated enallenes and B2pin2 in the carbocyclization.It was found that the adduct formed by the terminal vinyl of enallene coordinating to Pd（OAc）2 is the most stable.Thus,this adduct was set to be the zero reference point in our computations.The favorable mechanism is that under the catalysis of palladium acetate,the C-H bond of the enallene is activated to form a Pd-C bond,and the twoσbond rotations undergo ligand exchange to obtain an olefin-coordinating intermediate,which is favorable for the subsequent olefin insertion.After the olefin inserted,a carbocyclic intermediate is formed,and the product is obtained by boration of a carbon atom bonded to Pd.We also calculated the reaction energy barrier when the weakly directed group was changed to the strong directed group.The calculated overall barrier was too high and thus inconsistent with the experimental conditions because the strong Pd-N interaction hindered theσbond rotation.The origin of diastereoselectivity is still under investigation. |
