Exploring The Mechanism Of The Palladium-catalyzed 3-butene-2-ol Amination Reaction:A DFT Study

The amino reaction of alcohol is a kind of important organic chemical reaction.Its products are closely related to many fields through industry,such as medicine,chemical industry,materials,national defense,which have become an indispensable part of daily life.The amino reactions can be divided into four types according to the reactive environment that required for the reaction:(1)Direct amination mechanism / Carbocation reaction mechanism.(2)Mechanism of hydrogen transfer amination.(3)Coordination-nucleophilic amination reaction mechanism.(4)Mechanism of oxidation and hydrogen-transfer amination.Using alcohols as reactant also has many advantages,such as the low raw material cost,higher atomic utilization rate,good product selectivity and the environment-friendly by-product.In the present study,the mechanism for the palladium-catalyzed amination reaction of butenol in THF solvent was studied by density functional theory approach.The main contents are summarized as follows: The reaction studied in this paper has a high reaction energy in gas,which is extremely difficult to carry out;After the introducing of the polar solvent THF,the energy of the key step decreased and the reaction could proceed smoothly.In addition,due to the different attack directions of the nucleophile during the reaction,the chirality of the intermediate products could also be different.When the nucleophile attacks the substrate from the up-direction,the S chiral comformation intermediates can be produced.When the nucleophile attacks the substrate from the down-direction,the R chiral comformation intermediates can be produced.In this reactive process,the reaction energy barrier of forming the R chiral comformation intermediates is significantly lower than that to form the S chiral comformation intermediates.In other words,this means that the nucleophile attacking the substrate from the down-direction is the dominant reactive path,which result is consistent with the results that obtained form the experiment(there is a huge chiral products ratio difference in the reaction).On the basis of the above results,we further explored the influence of the chiral ligand on the reaction process.The catalyst ligands selected in the above reaction process were modified to have axial chirality with the original ligands,and then the research process was repeated.The results show that the dominant reactive route of the nucleophile has changed from the down-direction to the up-direction.Accordingly,the dominant product comformation of the reaction has also changed from the R comformation to the S conformation,which results might be helpful for the design and the modification for catalyst ligand to achieve the product separation purpose.Above research on reaction mechanism is not only helpful to understand the nature of the palladium-catalyzed butenol amination mechanism,but also of great guiding significance to the design of reactive routes and catalysts in related industries.