Theoretical Study On The Reaction Mechanism Of Rhodium-catalyzed CC Activation And CH Activation

Transition metal-catalyzed organic chemical reactions have attracted more and more attention and application recently.Especially for traditional organic chemical reactions with low atomic economy,preventing environmental pollution,improving energy economy,reducing by-products,and developing new catalysts have become the goals of researchers.The research on the mechanism of metal catalytic reaction can help us to design experimental reaction better,and provide theoretical support and guidance for experimental workers to develop new catalysts and improve atomic economy.We use quantum computational chemistry methods to explore the specific reaction mechanism in the experiment and the feasibility of experimental reaction in this article.The specific work is as follows:(1)According to density functional theory,we have calculated and studied the reaction mechanism of rhodium-catalyzed cycloisomerization of homopropargyl allene-alkynes to form tricyclic skeleton.The mechanism study showed that the three reactions A(Z=Me,X=^tBu),B(Z=Me,X=Me)and C(Z=H,X=Me)all experienced the initial oxidative cyclization reaction.Different cyclization and isomerization products will be obtained when different substitutions were used.From our calculations,we found that reactions A and B experienced alkyne insertion into Rh-C(sp2)bond and produced a key metal carbene intermediate.From the point of view of the metal carbene intermediate,the reaction A with large steric hindrance group(^tBu)is more inclined to 1,2-hydrogen migration to produce 6/5/4 tricyclic products;However,the reaction B with smaller sterically hindered group(Me)is more inclined to 1,2-carbon migration,and then ring expansion occurs and 6/5/5tricyclic products are produced.The reason of its regioselectivity can be attributed to steric effects.With regard to reaction C(Z=H,Z=H or Z=H,Z=Me),it is found that the elimination of?-hydrogen is more favorable than the insertion of alkynes into Rh-C(sp2)bond,so monocyclic products are obtained.It can be seen that the presence of dimethyl in allyl position is very important for obtaining tricyclic products.(2)According to density functional theory,we calculated and studied the reaction mechanism by the rhodium-catalyzed C-C activation of cyclopropanol to construct diketone or monoketone.It can be concluded that the catalyst[Cp*Rh Cl₂]₂ and additive Ag₂CO₃are very significant for the selectivity of products.By using[Cp*Rh Cl₂]₂ as the catalyst and Ag₂CO₃as the additive,the product is 1,6-diketone,whereas the?-hydride elimination product could not be obtained.Without[Cp*Rh Cl₂]₂,the product will become a monoketone.In addition,the combination of catalyst[Cp*Rh Cl₂]₂ and additive Ag OAc would also lead to monoketone.The observed selectivity is caused by the electronic effect.(3)According to density functional theory,we calculated and studied the reaction mechanism by the rhodium-catalyzed of C-H olefination of aromatic acids with unactivated olefins to achieve branched vinylated or linear allylated product.Based on our mechanistic study,this reaction includes four main steps:C-H bond activation,olefin migratory insertion,?-hydride elimination,and dehydrometalation.The position of the substituent group on the aromatic acid and different olefins would control the selectivity.Using NCI noncovalent interactions and dihedral angle analysis of key intermediate geometry,it is pointed out that steric effects are the fundamental reason for regioselectivity.In addition,the presence of the additive Na₂HPO₄ promoted the metal dehydrogenation process.