Theoretical Study On Some Triplet Silylenes And Silylenoids

This thesis mainly involves theoretical study on the structures,properities,and reactions of some triplet silylenes and silylenoids.1.Some new silylenes containing the N-heterocyclic carbenic?NHC?unit were investigated using M06-2X and QCISD methods.For these silylenes,the geometries of the singlet-and triplet-states were optimized and then the energies were calculated.The calculated results indicate that the energies for the triplet states are lower than the respective singlet states.Therefore,the ground states of these silylenes are triplet.The use of an NHC skeleton can increase the stability of thetriplet states.2.Some new silylenoids containing the N-heterocyclic carbenic?NHC?unit were investigated using M06-2X and QCISD methods.For these silylenoids,the geometries of the singlet-and triplet-states were optimized and then the energies were calculated.The calculated results indicate that the energies for the triplet states are lower than the respective singlet states.Therefore,the ground states of these silylenoids are triplet.The use of an NHC skeleton can increase the stability of the triplet states.At the same time,the insertion reactions of some triplet silyenoids with NH₃ and H₂O were investigated.3.The insertion reactions of the triplet silylenoid RB=SiLiF?R = CH₃,C₂H₅?with HF,H₂O,and NH₃ were studied using M06-2X and QCISD methods.The calculated results indicated that there are one transition state?TS?involving a three-membered-ring R-Si-H?R = F,OH,NH₂?and one intermediate?IM?connecting the corresponding reactants and products.The mechanism of all the insertion reactions of RB=SiLiF?R = CH₃,C₂H₅?with RH?R = F,OH,NH₂?is similar,but the degree of difficulty is not the same.Under the same condition,the insertion reactions should occur easily inthe following order:H-F> H-OH> H-NH₂.4.The insertion reactions in gas and solvent of the triplet silylenoid H₂SiAlCl₃ with RH?R = F,OH,NH₂,Cl,SH,PH₂?with HF,H₂O,and NH₃ were studied using M06-2X and QCISD methods.The calculated results indicated that RH molecules can be from two different position attack H₂SiAlCl₃ molecules to a further substitution reaction.And when RH molecules attack from the top of the Si-Al key,substitution reaction is more likely to happen.Solvation effects results show that the existenceof the solvent is not conducive tosubstitution.