Theoretical Study On The Mechanism Of Palladium-catalyzed Functionalization Of Unsaturated Compounds

Generally speaking,unsaturated compounds refer to compounds containing double,triple bond or benzene rings in chemistry.In this paper,useunsaturated compounds which containing carbon-carbon double bond and carbon-carbon triple bonds were mainly used.Functionalization of these unsaturated compounds is an effective way to construct C-C bonds and C-hetero bonds.Palladium complex is one of the most commonly used catalysts in transition metal reactions.Recently,palladium-catalyzed functionalization of unsaturated compounds has made great progress.In this paper,we use the density functional theory(DFT)method to study the reaction mechanism and selectivity of palladium catalysis.The results are divided into the following two parts:(1)The Cephalotaxus have a variety of biological activities and can produce natural products with various structures.The alkaloids contained in the roots,stems,leaves and seeds of this type of plant can effectively treat tumors,especially lymphosarcoma and lung cancer.It is an important wild plant with multiple uses and high economic value.The above skeletal structure can be quickly constructed by using palladium to catalyze the cascade reaction of aryl iodine,olefins and carbon monoxide through carbon-hydrogen activation.Through DFT calculation,we clarify the dominant reaction path of the reaction and the principle of selective control.The predominant mechanism of the reaction is to obtain metal-carbon bonds through Ar-I bond oxidation addition,carbon-carbon double bond insertion to obtain tetracyclic compounds,carbon monoxide insertion to form carbonyl groups,and Ar-H activation to obtain six-membered cyclic palladium intermediates.Finally,C(sp~2)-C(sp~2)reductive elimination was performed to obtain the prooduct.The Ar-H activation is a rate-determining step,and goes through the I~--assisted outer-sphere concerted metallization and deprotonation mechanism,the insertion of carbon-carbon double bonds is a selective-determining step and is irreversible.On the basis of our calculation of the superiority path,the stereoselectivity reported in the experiments has been well reproduced,verifying the rationality of our calculations.Further,we have discovered two modes in which the steric effects of substituents at three sites of the olefin substrate regulate the stereoselectivity of the reaction.The above studies have helped to understand the palladium-catalyzed cross-coupling reaction of unsaturated compounds and carbon monoxide,and in particular,provided rare research results on the stereoselective regulation of such reactions.(2)Phosphoryl-containing compounds have unique biological activities and are widely used in medicine,materials and other fields.These huge application values have made theresearch on this kind of substance popular.Here,we studied the mechanism and selectivity of palladium-catalyzed addition reaction of P(O)H compounds with alkynes by means of DFT studies.Calculation found that when two different phosphoryl-containing compounds are added to phenylacetylene,the same product can be obtained through different reaction mechanisms.When the reactants are phenylacetylene and phospholipids,the reaction mechanism is P-O oxidative addition,alkyne insertion,P-C isomerization,and P-C reduction elimination.However,when phosphoric acid were added,the reaction mechanism is the elimination of intermolecular hydrogen migration,ligand exchange,P-O isomerization,and P-C reduction.There are two kinds of selectivity in the reaction,Markovnikov addition and anti-Markovnikov addition.Computational studies have found that Markovnikov addition is predominant and the selectivity-determining step is alkyne insertion,and the rate-determining step is reduction reduction.