Theoretical Study On The Mechanism Of Palladium-catalyzed Telomerization Of 1,3-butadiene With Carbon Dioxide Or Isopropyl Alcohol

The telomerization reaction between 1,3-butadiene and nucleophiles has excellent performance in improving resource utilization,increasing economic benefits and reducing pollution because of its cheap and easy availability of raw materials,wide range of product uses,and extremely high atomic utilization.It has attracted considerable attention in the field of homogeneous catalysis for decades.The telomerization reaction of1,3-butadiene with CO₂not only fixes CO₂well to promote"carbon neutrality",but also obtains value-added chemicalsδ-lactone.The telomerization reaction of 1,3-butadiene with ⁱPrOH can generate 1,3,7-octatriene,an important chemical raw material,with high selectivity under certain ligand conditions.But so far,the mechanism of the above two reactions is still unclear,and the TON value obtained in the experiment is far from meeting the requirements of industrial production.The detailed study of its mechanism has important guiding significance for the further design of efficient ligand and catalytic systems.Based on this,this dissertation adopts density functional theory to study the mechanism of the above two reactions.We explore different reaction paths to find the most reasonable reaction mechanism,and explains the effect of substituents on the selectivity of the telomerization reaction of 1,3-butadiene and isopropanol.The main conclusions are as follows:（1）The mechanism of palladium-catalyzed telomerization reaction of 1,3-butadiene and carbon dioxide was systematically studied,and PTpOMe was selected as the ligand.It was found that palladium hydride played a key role in the reaction.Its mechanism mainly includes:1)olefin coordination;2)1,3-butadiene conformational transition;3)carbon-carbon coupling reaction;4)nucleophilic addition reaction;5)reduction and elimination reaction;6)palladium-hydrogen transfer reaction.Among them,the reaction rate-determining step is the nucleophilic addition elementary step.When CO₂and hydroquinone are associated,the energy barrier of the nucleophilic addition step is reduced,indicating that the addition of hydroquinone can promote the reaction to a certain extent.（2）The mechanism of palladium-catalyzed telomerization reaction between1,3-butadiene and isopropanol was systematically studied,especially the formation pathway of dimerization product 1,3,7-octatriene.It was found that the key step of1,3,7-octatriene formation is the palladium hydride transfer process.1,3-bis（2,6-diisopropylphenyl）-4,5-dimethyl carbene ligand（NHC-bisPr）and 1,3-bis（2,4,6-trimethylphenyl）-4,5-dimethyl carbene ligand（NHC-triMe）were selected,and their different effect on potential energy surfaces and the selectivity was discussed.It was found that the selectivigy of Pd-NHC-bisPr system is mainly controlled by thermodynamics,and it tends to produce dimerization product 1,3,7-octatriene along the PdH pathway.However,the selectivigy of Pd-NHC-triMe system is kinetically controlled,and tends to generate telomer product ethers along the C1 pathway.The additive ⁱPrONa plays an important role in this reaction.In the protonation elementary reaction,it interacts with ⁱPrO^-and effectively stabilizing the transition state,so that the energy barrier and reaction heat of the protonation elementary reaction are significantly reduced,and the apparent activation energy of the overall reaction is also reduced.