Mechanistic Insights Into the [3+1] Cycloadditions of Me₃SiN₃ on Bis‐Silylene and the Formation of Pseudo‐Silaazatriene

The reaction mechanism for the formation of the pseudo‐silaazatriene 1 (LN(SiMe 3 ) 2 −Si−N−Si(L)NSiMe 3 ; L=PhC−(N t Bu) 2 ) by the reaction of 1 equivalent of bis‐silylene (LSi−SiL; L=PhC(N t Bu) 2 ) with 3 equivalents of azide Me 3 SiN 3 has been explored at M06/def2‐TZVPP//BP86‐D3(BJ)/def2‐TZVPP level of theory. The reaction mechanism is guided by the high Lewis basicity of the silicon lone pair and the high Lewis acidic character of Si−N bonds, as well as by the high tendency to eliminate N 2 from Me 3 SiN 3 . The first step of the reaction is the formation of [3+1] cycloaddition product ( I1 ) by the synergetic interactions of the lone pair on the silylene silicon with the π* molecular orbital of Me 3 SiN 3 which is majorly localized on the terminal nitrogen atom, and the donation of the σ‐type lone pair on the nitrogen atom connected to the SiMe 3 group with the Si−N σ* orbital on silylene. The elimination of N 2 from I1 results in the formation of pseudo‐silaimine intermediate I2 having a dicoordinated, monovalent nitrogen atom. The most favourable pathway involves the second addition of Me 3 SiN 3 followed by N 2 elimination resulting bis‐silaimine intermediate I4‐P2 . The highly reactive lone pair on the dicoordinated, monovalent nitrogen atom can be coordinated to the Si−N σ* MO of the second silylene moiety resulting in Si−N bond formation and Si−Si bond cleavage. This step is similar to the S N 2′ reaction where the incoming nucleophile and the leaving group are on the same side resulting in the formation of silaimine I5 . Further, the [3+1] cycloaddition of one more molecule of Me 3 SiN 3 followed by N 2 elimination results in the formation of silaimine intermediate I7 . I7 undergoes 1,3‐silyl migration leading to the final product 1 . The lone pairs on di‐ and tricoordinated nitrogen centres of all the intermediates are stabilized by hyperconjugative interactions. The delocalized hyperconjugative interaction stabilizes the lone pairs in 1 .