Theoretical Study On The Diels-Alder Cycloaddition Reaction Catalyzed By Keggin-type Polyacid-supported Metal Single Atom

Diels-Alder（D-A）reaction shaped both the art and science of total synthesis to some degree.A large amount of biomass energy was derived into the admixture of D-A reaction,especially furan and furan derivatives.Therefore,D-A reaction provides a reliable way for efficient synthesis of aromatic monomer p-xylene（PX）.Due to the advances in DFT calculation in recent years,the computational research on polyoxometalates（POMs）based single-atom catalysts（SACs）is growing steadily,but until now there has been no research on the application of POMs-based SACs catalysts in D-A cycloaddition chemistry.A series of monatomic metals（M=Mn,Fe,Co,Ru,Rh,Pd,Os,Ir,Pt）were supported by PTA=[PW₁₂O₄₀]^3-.The D-A cycloaddition reaction of C₂H₄ and C₄H₆,the D-A cycloaddition reaction of C₂H₄ and 2,5-DMF and the subsequent dehydration process have been studied.The research includes:（1）The determination of M₁/PTA（M=Mn,Fe,Co,Ru,Rh,Pd,Os,Ir,Pt）by DFT-M06l;The D-A cycloaddition reaction of C₂H₄ and C₄H₆ catalyzed by PTA=[PW₁₂O₄₀]^3-)SACs was calculated theoretically.The calculated adsorption energy for C₄H₆ is greater than that for C₂H₄.The D-A activation energy barrier of Pd₁/PTA(8.38kcal mol^-1)was the smallest in all the systems,and it had the potential of catalytic D-A reaction.The catalytic activities of all metal systems were investigated at different temperatures,and the activation energy barrier increased with the increase of temperature.The MOs electronic structure of Pd₁/PTA indicated that the high catalytic activity was due to the high overlap between the d orbital and theπorbital of C₄H₆,which improved the stability of the bonding orbital and promoted the catalytic activity of the D-A cycloaddition reaction.（2）Based on（1）,the D-A cycloaddition reaction of M₁/PTA SCAs to C₂H₄ and2,5-DMF and the dehydration process of oxidized norbornene cycloadduct were investigated.Compared with the system without catalyst,the activation energy barrier of Ru₁/PTA SCAs was reduced by 11.77 kcal mol^-1,which was mainly attributed to the proximity of the d-band center to Fermi level during the interaction between the metal monatom and C₂H₄,which reduces the electron filling of the anti-bonding orbital and improves the adsorption stability energy of C₂H₄.So it speeds up the D-A reaction.Ru single atom has a high contribution rate of 81.1%to the bonding orbital between catalyst and norbornene oxide cycloadduction product,which enhances the stability energy of cycloadduction product.The activation energy barrier of C-O fracture was the highest in the process of dehydration aromaization of nobornene oxide by M₁/PTA SCAs,which was the decisive step in the dehydration process.Ru₁/PTA SCAs reduced the reaction energy barrier to 21.49 kcal mol^-1,which enhanced the catalytic effect and reduced the loss and separation of intermediates.Theoretical design of efficient bifocal catalyst for D-A and dehydration reaction in series.