Theoretical Study On Phosphine-Catalyzed Annulation Reactions Of Saturated Amines And Allenoates

With the fast development of computer technology and the improvement of computational methods,theoretical calculation,which is an effective method to study the nature of chemical reactions,has played an irreplaceable role in exploring the mechanism of catalytic reactions and the origin of selectivity.In this thesis,the cyclization reaction of allene and saturated amine catalyzed by organic phosphine has been systematically studied by performing quantum chemical calculations.In the first chapter of this thesis,we briefly introduce the development background of computational chemistry,several commonly used theoretical analysis methods,the organophosphine catalysts and organophosphine catalyzed cyclization reactions of allenes.In the second chapter of this thesis,the[3+2]cyclization reaction of allenoate and saturated amine catalyzed by triphenylphosphine/chiral phosphine catalyst has been selected as the research object,then their detailed mechanism and the origin of chemo-and stereoselectivity were systematically studied by using density functional theory(DFT).In the third chapter,we used the DFT method to study the pyrolysis reaction of the biphosphirane metal complex,and discussed the possible mechanisms and the activity of the intermediate involved in the reaction.The following is the abstracts for the two reactions:In chapter 2,we used the density functional theory method to calculate the three possible pathways for the cyclization reaction of δ-acetoxy allenoate and 2-Sulfonamidomalonate catalyzed by triphenylphosphine/chiral phosphine catalyst,including[α,γ]-[3+2]cyclization pathway,[δ,β]-[3+2]cyclization pathway,and[α,δ]-[4+2]cyclization pathway.The calculation results show that the[α,γ]-[3+2]cyclization pathway is the most energetically dominant pathway.The entire catalytic reaction process consists of eight steps:(1)the adsorption process of organophosphine and allenoate,(2)the dissociation process of AcO-group,(3)the deprotonation process of saturated amine,(4)nucleophilic attack by the deprotonated amine anion to the electrophilic phosphonium diene intermediate,(5)[1,6]-proton transfer process,(6)five-membered N-heterocyclic ring-closure process,(7)HAc-assisted[1,2]-proton transfer process,(8)the desorption of the catalyst and the formation of the 3-pyrroline product.In addition,the calculated results show that the fourth step is not only the chemoselectivity-determining step,but also the stereoselectivity-determining step,and the pathway associated with the generation of the R-configuration product is the most energetically favorable pathway,which is consistent with the experimental results.By analyzing the structure,it is found that the chemoselectivity of the reaction is mainly controlled by the steric hindrance in the ring-closure transition states involved in the three different pathways.Further non-covalent interaction(NCI)and atomic theory in molecules(AIM)analyses showed that the C-H…O hydrogen bond interaction is the key factor for controlling the stereoselectivity of the reaction.This research can not only help people understand the general mechanism of the[4+2]and[3+2]cyclization reactions of allenoate and saturated amines catalyzed by organophosphines,but also provide necessary theoretical guidance for the design of organophosphinecatalyzed cyclization reactions with high chemoselectivity and high stereoselectivity.In chapter 3,we used the density functional theory method to calculate the three possible pathways for the thermal pyrolysis reaction of biphosphirane-M(CO)x(M=Mo,Cr,W and Fe;X=4,5)complexes,including pathway a,pathway b,and pathway c.In pathway a,(PC2H4)2-M(CO)x undergoes a ring expansion process to generate 3,4dihydro-1,2-diphosphete P2C2H4-M(CO)x four-membered ring intermediate.Pathway b is that the(PC2H4)2-M(CO)x complex is converted into 3,4-dihydro-1,2-diphosphete P2C2H4-M(CO)x intermediate by releasing ethylene and cyclization.In pathway c,(PC2H4)2-M(CO)x is transformed into the diphosphorus P≡P-M(CO)x intermediate by releasing two molecules of ethylene.The calculation results show that the two stepwise reaction pathways b and c are more energetically favprable than the concerted reaction pathway a in kinetics,and both intermediates can be obtained in the experiment.Then,we systematically studied the reactivity of active intermediates coordinated by different metals,including 3,4-dihydro-1,2-diphosphete-M(CO)x and diphosphorus-M(CO)x(M＝Mo,Cr,W and Fe;X=4,5).The frontier molecular orbital(FMO)analysis shows that the overlap/interaction between the d orbital of the coordinated metal atom and the p orbital of the phosphorus ligand forms a π-bonded orbital.Further molecular electrostatic potential(MEP)and electronic local function(ELF)analyses indicated that the two phosphorus atoms in the active intermediate can be used as nucleophilic and electrophilic active sites,respectively.These research results can provide a theoretical basis for the rational design of the conversion reaction involving these two active intermediates with nucleophilic or electrophilic properties in the future.The fourth chapter of this thesis is a summary of all the above theoretical researches and prospects for futural work.