Novel Silaketenimines And Its Derivatives:Theoretical Prediction、Chemical Bonds Analysis

Silylenes（R2Si:）is a carbene analog of silicon and a very important intermediate in organosilicone chemistry.The ground state of silylene is singlet,because its electronic structure contains a lone pairs of electrons and an empty p orbital,therefore,it has a dual property:Lewis basic and Lewis acidic.It can be used as a syntheton for allenic derivatives,and allenic derivatives have been synthesized and separated,such as（R₂Si=C=CR₂）.For the allenic derivatives replaced by heteroatoms,such as（RSi=C=XCH₃,X=N,P,As）,there are currently less than 10 single crystal structure verifications,and their reaction properties are also poorly studied.In this thesis,the structure of silylenes-methylisocyanitrile adduct 1～44（R₂SiCNCH₃）,phosphine and arsenic analogues 1’～20’（R₂SiCPCH₃）and 1’’～20’’（R₂SiCAsCH₃）was mainly predicted by theoretical calculation.On this basis,the electronic structure was analysed by NBO theory and EDA-NOCV theory,and some novel silaketenimines were obtained.The main research contents of this thesis are as follows:1.Using theoretical chemical research methods,the structure of silylenes-methylisocyanitrile adduct（compounds 1～44）was optimized,and NBO analysis was carried out on this basis.The results show that this kind of compound has two main resonance structures A and B（Figure 1-21）:compounds 1～20,22 and 25 are silaketenimines（R₂Si=C=NCH₃）,the molecular structure contains allenic double bonds,the methyl isonitrile fragment has a certain amount of negative charge,and the resonance structure A is its dominant electronic structure.Compounds 21,23,24,26～44are 1,3-dipole compounds（R₂Si^--C≡N⁺-CH₃）formed by the addition of silylene and methyl isonitrile,which contains positive and negative charges at both ends of the electronic structure in the local structure of the molecule,methyl isonitrile fragments with a certain amount of positive charge,resonance structure B is its dominant electronic structure,the above conclusion can be proved by NBO directional search data.On the other hand,EDA-NOCV analysis was also carried out for compounds 1～44,and for silaketenimines,the orbital interaction between silylene fragment and methylisocyanitrile fragment was greater than the electrostatic interaction,which can also indicate that the component of covalent bond between silicon-carbon bonds is greater than that of ionic bonds.For 1,3-dipole compounds,the orbital interaction between silylene fragments and methylisocyanitrile fragments is smaller than electrostatic interaction,which can also indicate that the components of covalent bonds between silicon-carbon bonds are smaller than those of ionic bonds,and EDA-NOCV analysis further supports the results of structural optimization data and NBO analysis.In summary,the dominant structure of compound 1～44 can transition from resonant structure A to resonant structure B,because the electronegativity of the substituent connected to the silicon atom is increasing,which leads to the gradual decrease of the negative charge of the methyl isonitrile fragment and the gradual increase of the positive charge.2.Using the optimized structural data and NBO analysis results of phosphine and arsenic analogues of silaketenimines（R₂Si=C=PCH₃,R₂Si=C=AsCH₃）,it can be concluded that they are all allenic double-bonds compounds.Through NBO directional search,it was found that the main resonance structure of phosphine and arsenic analogues of silaketenimine contained resonance structure A,and its electronic structure was close to resonance structure A.The phosphine and arsenic analogues of silaketenimine contain less resonance structure B in the main resonance structure.