| Organometallic chemistry,as a subject formed by the intersection of inorganic chemistry and organic chemistry,has attracted much attention in the fields of organic synthesis,material preparation,energy development and environmental protection.In recent years,based on the synthesis strategies of adding oxidants,designing efficient catalysts and developing new catalytic systems,great progress has been made in transition metal-catalyzed and photoredox/transition metal-cocatalyzed coupling reactions among electrophiles/nucleophiles,nucleophiles/nucleophiles and electrophiles/electrophiles,which have become a key area of research for chemists.By calculating and analyzing the structure,energy,electronic effect and steric effect of key intermediates and transition states in the reaction process,theoretical computational chemistry can deeply understand the reaction mechanism,reactivity and selectivity,which has important theoretical guiding significance for designing new catalysts and developing new synthesis methods in experiments.In this paper,several typical C-C coupling reactions among electrophiles/nucleophiles,nucleophiles/nucleophiles and electrophiles/electrophiles have been studied systematically through density functional theory(DFT),aiming to clarify the characteristics and esscence of different types of C-C coupling reactions and providing a theoretical basis for the construction of different types of C-C bonds in experiments.The main research contents of this paper include the following four parts:1.Ligands mediated Au-catalyzed 1,2-diarylation of aryl alkenes with aryl iodine and the cross-coupling of arene with aryl iodine were studied.For the(P,N)ligand Me-Dalphos mediated Au-catalyzed 1,2-diarylation of aryl alkenes with aryl iodine:the calculated results show that the π-activation mechanism is more favorable than the migratory mechanism,which involves olefin coordination to Au1,oxidative addition of aryl iodine to Au1,electrophilic cyclization of olefin,deprotonation and C-C reductive elimination five key steps.The oxidative addition is the rate-determining step and electrophilic cyclization is the regioselectivity-determining step.The electrophilic attack of different olefin carbons on aromatic carbon determines the regioselectivity of the reaction,in which the electrophilic attack of C2 atom on aromatic carbon to form six-membered ring exo-type product is more favorable,while the electrophilic attack of C1 atom on aromatic carbon to form seven-membered ring endo-type product is less favorable.In addition,we also studied the effect of different(P,N)ligands on the reactivity.The results show that the strong electron-donating ability of-Ad and-NMe2 groups facilitates the transformation of AuⅠ to AuⅢ,while the strong electron-withdrawing ability of-Ph and-PhN groups supresses the transformation of AuⅠ to AuⅢ,resulting in lower reactivity.For the N-heterocyclic carbene ligand ImPyNMe2 mediated Au-catalyzed cross-coupling of arene with aryl iodine:the calculated results indicate that the reaction mechanism mainly includes oxidative addition of aryl iodine to the AuⅠ center,C-H activation of arene and C-C reductive elimination,in which C-C reductive elimination is the rate-determining step.Moreover,the structure and energy analyses of the C-C reductive elimination transitions states show that the-NMe2 on the C5 position of N-heterocyclic ligand is crucial.The nitrogen atom of-NMe2 coordinates to AuⅢ center and donate 2 electrons,reducing the barrier energy of rate-determining step and facilitating the process.2.Chiral phosphine ligand mediated Cu-catalyzed selective addition of 1,4-pentadiene with acetophenone to obtain linear 1,3-diene was studied.The calculations find that the reaction proceeds via three main steps:σ-bond metathesis of 1,4-pentadiene with Cu(Ⅰ)catalyst,nucleophilic addition of allyl to acetophenone and σ-bond metathesis of 1,4-pentadiene with Cu(I)alkoxide.The first step controls the reaction rate and the third step controls the regioselectivity and stereoselectivity.The results show that the formation of linear 1,3-diene product is 11.3 kcal/mol more favorable than the branched 1,3-diene product.Configurational analyses show that the steric effect is the key factor controlling Z/E selectivity.In the transition state to obtain E-selective product,there is a larger steric repulsion between the vinyl group of 1,4-pentadiene and the phosphine ligand,which is not conducive to the formation of E-selective product.IGM analyses show that when using(R)-DTBM-SEGPHOS ligand,the π-π interaction between the phenyl group of substrate acetophenone and the phenyl group of phosphine ligand in the R-type transition state is stronger than that in the S-type transition state,thus the formation of R-type product is more favorable,while when using the(R,R)-Ph-BPE ligand,there are both CH…π interaction and π-π interaction between substrate acetophenone and phosphine ligand in the S-type transition state,but there is onlyπ-π interaction between substrate acetophenone and phosphine ligand in the R-type transition state,thus the formation of S-type product is more favorable.3.Pd-catalyzed oxidative cross-coupling of 1,2-allenyl ketones with aryl boronic acid was studied.The calculated results show that the reaction mechanism is affected by the substituents of allenyl groups in 1,2-allenyl ketone:when the R1 and R2 substituents of allenyl groups are phenyl and methyl respectively,the π-allyl-Pd(Ⅱ)intermediate path competes with the Pd(Ⅱ)-carbene intermediate path and the π-allyl-Pd(Ⅱ)intermediate path is more favorable thermodynamically,while when the R1 and R2 substituents of allenyl groups are hydrogen atoms,the Pd(Ⅱ)-carbene intermediate path is the dominant path.The synergistic transformation mechanism of Pd(0)to Pd(Ⅱ)was proposed.It is found that the transformation from Pd(0)to Pd(Ⅱ)is carried out through a synergistic oxidative transmetalation process rather than stepwise oxidation-transmetalation process.In addition,we also calculated the influence of substrate substituents on the reactivity.The results show that when the substituents of the allenyl group are phenyl and methyl,the π-allyl-Pd(Ⅱ)and Pd(Ⅱ)-carbene intermediates paths both contribute to the formation of the product.However,when the substituents of the allenyl group are hydrogen atoms,the π-allyl-Pd(Ⅱ)intermediate path is not feasible due to the formation of a stable π-allyl-Pd(Ⅱ)intermediate,so the reaction can only proceed through the Pd(II)-carbene intermediate path,resulting in lower yield.4.IrⅢ/NiⅡ-metallaphotoredox-catalyzed difluoromethylation of aryl bromides was studied.The calculated results show that the reaction occurs synergically through a photoredox catalytic cycle and a nickel catalytic cycle.The former involves reductive quenching of*IrⅢ(IrⅢ/*IrⅢ/IrⅡ/IrⅢ),the latter uses Ni0 as the catalytic active component and obtains the difluoromethylation product through Ni0/NiⅠ/NiⅢ/NiⅠ/Ni0 or NiO/NiⅡ/NiⅢ/NiⅠ/Ni0 path.It is found that the active catalyst Ni0 species is produced from the initial catalyst NiⅡspecies by two consecutive reductive quenching of IrⅡ species.In addition,the effect of CHF2Br stoichiometric ratio on the reactivity of aryl bromides with different substituents is elucidated qualitatively.The orbital analysis show that the stronger the electron-withdrawing ability of the substituents on the aryl bromide,the oxidative addition of aryl bromide to NiⅠ is easier.Therefore,the excess CHF2Br will compete with para-fluoro substrate with weak electron-withdrawing ability,resulting in lower yield,but will not compete with cyanopyridine bromide with strong electron-withdrawing ability,and the yield increases with the increase of CHF2Br.The competition between the excess CHF2Br and para-trifluoromethyl substrate is relatively weak,thus the yield increases first and then decreases. |
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