Theoretical Study On Palladium-Catalyzed Multicomponent Synthesis Of Five-and Six-membered Ring Compounds

With the development and progress of society,organometallic chemistry has gradually developed as a very popular field in organic chemistry in recent years.Nowadays,homogeneous transition metal complexes have become a new type of catalysts exhibiting excellent reactivity and selectivity in chemical reactions,and has been widely used in many fields and disciplines.In recent years,with the rapid improvement of computer power and the development of first-principles calculation methods,the computer simulations can be used to explain the experimental results and phenomena that cannot be explained by general chemical rules with a clear and correct understanding of the reaction mechanisms.The theortical studies on reacrion mechanism and deep understanding for the nature of reactions are of great significance for the further development and application of modern chemistry.In this dissertation,we performed a series of theoretical studies on palladium-catalyzed multicomponent synthesis of five-and six-membered ring compounds.By the density functional theory method,the reaction mechanism,reaction characteristics,and the role of solvents and bases on the reaction process are revealed at the molecular level for deep understanding of this kind of activation reactions.It provides an important theoretical reference for the subsequent design of better synthetic pathways and the development of higher performance catalysts and new synthetic materials.The main innovations achieved in this dissertation are listed as follows:1)The reaction mechanism of palladium?0?-catalyzed reaction of aryl iodides,norbornene,and di-tertbutyldiaziridinone has been studied theoretically.Two reaction mechanisms were calculated.The reaction mechanism involving Cs₂CO₃combination first followed by alkene insertion is calculated to be preferred to the one in which alkene insertion occurs first followed by Cs₂CO₃ combination.The calculations suggest that the reaction proceeds via C-I bond oxidative addition,CsI·CsCO₃ cluster anion formation,alkene insertion,C-H bond activation,N-N bond oxidative addition,and two successive C?sp²?-N bond-forming,and C?sp³?-N bond-forming reductive elimination steps.The N-N bond oxidative addition involves the rate-determining transition state with a free energy barrier of 29.4kcal/mol.The role of base Cs₂CO₃ played during Cs I·CsCO₃ cluster anion formation and N-N bond oxidative addition process has been discussed according to the formation of relatively strong Pd-O bond.The role of base K₂CO₃ has been calculated and compared with Cs₂CO₃.2)The reaction mechanism of palladium-catalyzed allyl-substituted3,4-dienoate,alkyne and carbon monoxide to form ynone has been theoretically investigated by using density functional theory calculations.Two reaction mechanisms have been calculated.In one reaction mechanism,the C?sp³?–H bond of allyl-substituted 3,4-dienoate is frst activated while the C?sp?–H bond of alkyne is frst activated in the other reaction mechanism.It is found that the activation of C?sp?–H bond of alkyne is superior to C?sp³?–H bond activation of allyl-substituted3,4-dienoate.The calculations suggest that the reaction mainly proceeds via C?sp?–H bond activation,CO insertion,alkene insertion,second CO insertion,allene C=C insertion and C?sp³?–H bond activation steps.The transition states of alkene insertion and CO insertion into Pd–C?sp³?are competitive as the rate-determining transition state with a free energy barrier of around 23 kcal/mol.Moreover,it is found that the CO molecule does not directly participates in the reaction but also acts as an ancillary ligand.In addition,the reaction mechanisms for formation of other side products have been calculated and compared.3)The reaction mechanism of palladium?0?-catalyzed reaction of o-iodoanilines,CO2,and CO has been studied theoretically.The calculations suggest that the reaction proceeds via C?sp²?-I bond oxidative addition,CO insertion,Cs I·OAc cluster anion formation,N-H bond activation,ligand exchange of one PPh₃ ligand with CsI·HOAc cluster,CO₂ insertion,and C?sp²?-O bond reductive elimination steps.The CO₂ insertion involves the rate-determining transition state with a free energy barrier of 18.4 kcal/mol,consistent with the experimental reaction condition?60°C?.The influence of solvent on the reaction mechanism was analyzed.It is found that the CO₂ insertion occurs with the coordination of PPh₃ ligand in THF while it needs the help of base CsOAc in toluene.The role of bases KOAc and NaOAc has been calculated and compared with CsOAc.When the radius of the metal atom decreases in the order Cs>K>Na,the stability of the rate-determining intermediate increases,resulting in the increase of the reaction energy barrier.