Theoretical Studies On Noble Metal Catalyzed Hydroalkynylation Of Allenamides And Cyclization Of Benzodioxin

Transition metal has become the most common catalyst in the field of modern organometallic chemistry with its advantages of high selectivity and high reactivity.Transition metal complexes also have high catalytic activity for hydrogenation and dehydrogenation reactions.They are often used as hydrogenation and dehydrogenation catalysts in industrial production.Some transition metal catalysts can be modified and integrated to participate in the reaction in the form of supported catalyst,block catalyst,alloy catalyst,etc.,which greatly improves the application performance and scope of application of metal catalysts.And transition metal catalysts are also popular in the fields of environmental science,life science,energy chemistry and polymer chemistry.Although transition metal catalysis has developed rapidly in experiments,its theoretical research has developed slowly.The experimental mechanism of some transition metal catalyzed systems is not clear,and some experimental phenomena can not be explained because of the unclear microscopic process of the reaction,which greatly hinders the further development and improvement of transition metal catalyzed organic reactions.Therefore,it is very important to use the research methods of quantum chemistry and the calculation software to simulate the molecular participation in the reaction so as to explore the micro mechanism of the reaction,which is helpful to understand the nature of the reaction and guide the improvement of the reaction.In this paper,based on actual experiments,two experimental systems using transition metals palladium and gold as catalysts were selected for theoretical research.With the aid of density functional theory,the reaction mechanisms involving transition metals were calculated at the molecular level.The reasons for the selectivity of ligand regulation,the reasons for the ratio and amount of catalyst to determine the yield were explained,and the thermodynamic and kinetic results were analyzed and explained.It has deepened people’s deeper understanding of the hydroalkynation reaction of allene and the cyclization reaction catalyzed by gold,and also provided a certain theoretical reference for further improving the efficiency of the reaction by improving the catalystThe main research contents and results of this paper are summarized as follows:1.The reaction systems of allenamides to form 1,3-and 1,4-enynes under the palladium catalysts with different ligands were studied.The experimental results show that the system involving the BrettPhos ligand gives 1,4-enyne and the system involving(o-OMePh)3P ligand gives 1,3-enyne.Moreover,the reaction speed of the system involving(o-OMePh)3P ligand was about 6 times that of the BrettPhos ligand system.In order to get a reasonable explanation of the experimental phenomenon,we performed calculations using density functional theory.Calculations show that no matter whether BrettPhos or(o-OMePh)3P ligands are used,the palladium-catalyzed hydroalkynation of allenamides to synthesize 1,3-and 1,4-enyne is via the hydropalladation mechanism,rather than the carbopalladation mechanism,as proposed for the formation of 1,4-enyne in the experimental study.BrettPhos ligand contributes to the formation of 1,4-enyne by the anti-Markovnikov addition of Pd-H bond to the C=C bond,but(o-OMePh)3P ligand form 1,3-enyne by the Markovnikov addition.The results of distortion/interaction analysis and noncovalent interactions(NCIs)analyses also support the calculation results of DFT.According to the calculated energy barrier,the BrettPhos ligand system is 1.2 kcal/mol higher than the(o-OMePh)3P ligand system,which is also consistent with the reaction rate BrettPhos ligand:(o-OMePh)3P ligand=1:6.The results of the kinetic experiments were confirmed.Palladium catalysts also promote the isomerization of E-1,3-enyne,which reasonably explained the observed stereoselectivity.2.The system of Au-catalyzed cyclization of benzodioxin derivatives to isocoumarin was studied by density functional theory.In the experiment,there is no yield when the catalyst is(Ph3P)AuCl or AuCl.The yield is low when AgSbF6 is used as the catalyst.The product yield is highest when(Ph3P)AuCl and AgSbF6 coexist as the catalyst.To explain why the type and proportion of experimental catalysts affect the yield,we first selected the system of equal(Ph3P)AuCl and AgSbF6 as catalysts to find a reasonable reaction path,including nucleophilic cyclization,ring-opening process(slowest step)and catalyst reduction process.Then the fact that the yield is further improved by adding an additional AgSbF6 is also consistent with our calculated energy barrier.We speculate that in a system of Π activation of unsaturated double bonds by gold,additional AgSbF6 act as a co-catalyst for σ activation of carbonyl groups,while the Π activation capacity of AgSbF6 may be a little worse than that of gold.When the(Ph3P)AuCl or AuCl of the linear structure exist alone,the reaction is difficult to occur because the difficult departure of Cl-reduces the catalytic ability of gold.Through theoretical research,we reasonably explained the experimental phenomena and also helped to understand the gold-silver co-catalysis system.