Reaction of a Disilyne with Internal Alkynes: Reversible [1 + 2] Cycloaddition and Formation of Strained Unsaturated Silacycles

The reactions of NHB-stabilized disilyne (NHB)Si≡Si(NHB) (1, NHB = [ArN(CMe)₂NAr]B, Ar = 2,6-ⁱPr₂C₆H₃) with internal alkynes were described. Reaction of disilyne 1 with one equivalent of bis(trimethylsilyl)acetylene led to a reversible [1 + 2] cycloaddition of one of the Si atoms with the alkyne and the insertion of the other Si into one of Ar rings with the formation of a silirenyl–silepin 2, whereas reaction of 1 with two equivalents of Me₃SiCCSiMe₃ resulted in the formal addition of the C_sp–Si bond to the Si≡Si triple bond to give disilene (NHB)(Me₃Si)Si=Si(CCSiMe₃)(NHB). Reaction of 1 with 1,3-diyne Me₃SiCCCCSiMe₃ yielded a 1,2-disilacyclobut-3-ene via cycloaddition, ring expansion, and NHB 1,2-shift sequence. The initial [1 + 2] cycloaddition of one of the silicon atoms with an alkyne was strongly supported by DFT calculations. The results demonstrated the significant bis(silylene) character and rich synthetic potential of bis(boryl) disilyne 1.