Computational Studies On Mechanisms Of Transition Metal-Catalyzed Methylenecylopropanes (MCPs) Involved Organic And Polymerization Reactions

Methylenecyclopropane derivatives(MCPs)have been widely used in organic synthesis as well as in polymerization,because they have highly strained structure with olefinic group attached to three-membered ring.In recent years,many researchers have explored synthetic organic reactions of methylenecyclopropane derivatives using transition metal as catalysts to synthesize various compounds with functional groups.Transition metal-catalyzed methylenecylopropanes involved reactions include addition,ring-opening,rearrangement and others.Due to diverse active sites present in methylenecylopropane,various mechanistic pathways are possible for transition metal-catalyzed methylenecylopropanes involved reactions showing that such mechanisms are substrate-dependent.However,mechanisms of transition metal-catalyzed reactions of methylcyclopropanes still remain unclear.Therefore,it is worthy to investigate the mechanisms of methylcyclopropanes involved reactions,which would be helpful in the design and synthesis of new compounds.In this thesis,density functional theory(DFT)method was used to study the mechanisms of transition-metal-catalyzed MCPs related organic and polymerization reactions.The computational study revealed several possible initiation pathways(i.e.three-membered-ring of MCPs activation routes,C-C double bond activation routes and other substrates activation routes).Afterwards,the chemoselectivity and regioselectivity of MCP involved reactions were investigated.The effect of substituents,electronic factors and steric hindrance were also considered.Based on this research,valid inferences can be made from the mechanisms of transition-metal-catalyzed methylenecylopropanes(MCPs)involved organic and polymerization reactions.The research details are summarized as follows:(1)Computational studies were carried out to investigate the detailed mechanisms of Pd(0)-catalyzed intermolecular and intramolecular hydroamination of MCPs.The initial activation of the three-membered ring of MCPs would readily occur via the insertion of Pd(0)into the distal C-C bond,generating a metallacyclobutane intermediate.The commonly proposed oxidative addition of nucleophile(Nu-H)onto the Pd(0)center to afford a hyrido-Pd(II)complex,however,is less favorable in comparison with the Pd(0)mediated cleavage of the distal C-C bond of MCPs.Subsequently,for the Pd(0)-catalyzed intermolecular hydroamination of 1,1-diphenyl MCP with 2-pyrrolidone,it is more favorable for C1 of the metallacyclobutane intermediate to undergo proton transfer from an incoming amide to yield a ?-allylpalladium intermediate,from which the final allylamine product is afforded via reductive elimination.For the Pd(0)-catalyzed intramolecular hydroamination of aniline-tethered MCP,the intramolecular nucleophilic attack of the amine moiety to C3/C4 of the corresponding metallacyclobutane intermediate is preferred,thus generating a cyclized intermediate.Subsequent proton transfer step would follow to complete the hydroamination reaction.In this work,the preference for the hydrogen transfer pathway and the nucleophilic attack pathway in Pd(0)catalyzed hydroamination of MCPs were revealed.(2)Computational studies were carried out to investigate the mechanisms of gold-catalyzed ring-opening of methylenecyclopropanes(MCPs)and vinylcyclopropanes(VCPs),respectively,with sulfonamides to afford homoallylic amine intermediates,which would subsequently produce pyrrolidine derivatives.The detailed activation modes of MCPs,mediated by the Au(I)catalyst were comprehensively explored.Computational results suggest that the activation of MCP by the Au(I)catalyst is less feasible kinetically and thermodynamically.Instead,the Au(I)catalyst mediated activation of sulfonamides could result in the increased acidity of the N-H bond,which is ready to undergo intermolecular proton transfer to the C=C moiety of MCP to form a cyclopropylcarbinyl cation intermediate.Subsequently,the nucleophilic attack of the formed amido group to the three-membered ring moiety of the yielded cyclopropylcarbinyl cation intermediate in an SN2 manner would follow to afford the ring-opening homoallylic sulfonamide.In addition,computational studies indicate that such mechanistic pathway could also apply to the VCPs involved hydroamination with sulfonamides.The mechanism of triflic acid catalyzed hydroamination of MCPs and VCPs with sulfonamides also proceeds via the cyclopropylcarbinyl cation intermediates,formed by the protonation of the alkene moiety of MCPs and VCPs,respectively.The ineffectiveness of amines as amination reagents in the Au(I)-catalyzed hydroamination of MCPs and VCPs was discussed.(3)Computational studies were carried out to investigate the mechanism of Pt-catalyzed silaboration of methylenecyclopropanes(MCPs)with silyboronic ester via site-and regioselective C-C cleavage of cyclopropane ring to afford organoboron and organosilicon compounds.Two MCP substrates were considered in this work.Both MCPs-activation-first mode and silyboronic ester-activation-first mode were investigated.Calculation results suggest that MCPs-activation-first mode by the catalyst is less feasible while the oxidative addition of Pt(0)with silylboronic esters showed to be favorable.Afterwards,migratory insertion of MCPs could take place followed by ?-carbon elimination,thereby affording the ring-opening organoboron intermediate,which could undergo reductive elimination to generate the corresponding product.The regioselectivity in the reaction is controlled by the bulkiness of the boron group in the migratory insertion step.A detailed mechanistic pathway leading to the corresponding product was proposed.(4)Computational studies were applied to investigate the mechanisms of Pd/Ni-catalyzed polymerization of MCPs.The detail initiation strategies for Ni-catalyzed addition polymerization and Pd-catalyzed ring-opening polymerization were revealed in this work.For Ni-catalyzed addition polymerization,the calculation results showed that the chain-propagation step takes place via repeated 2,1-migratory insertion of the monomer.However,the ring-opening step would occur by the addition of PPh3 and Ag OTf.The calculation results suggested that the initiation process starts form either 1,2-or 2,1-migratory insertion of the monomer.When 1,2-migratory insertion of the monomer takes place,?-carbon elimination would follow to generate the ring-opening intermediate.When 2,1-migratory insertion of the monomer occurs,insertion of the monomer would follow without the ring-opening step.On the other hand,for Pd-catalyzed ring-opening polymerization,the initiation step would take place via 2,1-migratory insertion of monomer followed by ?-carbon elimination to form the ring-opening intermediate.The selective insertion of the monomer in the initiation step was investigated in detail.Afterwards,a detailed mechanistic pathway leading to the corresponding product was proposed.Based on the theoretical findings mentioned above,it is expected that the unprecedented mechanism proposed herein would help to deepen the understanding of the mechanisms of methylenecylopropanes(MCPs)related organic and polymerization reactions.