Homocoupling of Isocyanide at the Si(II) Center of Borylaminoamidinatosilylene

Two borylaminoamidinatosilylenes (L)[(1,5-C₈H₁₄)B(Ar)N]Si (L = PhC(NtBu)₂, Ar = 2,6-iPr₂C₆H₃ (1)) and (L)[(1,5-C₈H₁₄)B(Ar')N]Si (Ar' = 2,4,6-Me₃C₆H₂ (2)) have been prepared and utilized to investigate the reaction toward isocyanide. Reactions of 1 with the respective CN-2,6-Me₂C₆H₃ and CNCy (Cy = cyclo-C₆H₁₁) produced compounds (L)Si(NAr)C(N-2,6-Me₂C₆H₃)B(1,5-C₈H₁₄)(CN-2,6-Me₂C₆H₃) (3) and (L)Si(NAr)C(NCy)C(NCy)B(1,5-C₈H₁₄)(CNCy) (4). Reactions of 2 with the respective CNCy and CN-2,6-Me₂C₆H₃ yielded compounds cyclo-(L)SiN(Ar')C(NCy)B(1,5-C₈H₁₄)C(NCy) (5) and cyclo-(L)[(1,5-C₈H₁₄)B(Ar')N]SiC(CN-2,6-Me₂C₆H₃)N(2,6-Me₂C₆H₃)C(N-2,6-Me₂C₆H₃) (6). Compounds 3-6 have different compositions and structures from each other. Density functional theory (DFT) calculations suggest initial formation of (L)[(1,5-C₈H₁₄)B(←:CN-2,6-Me₂C₆H₃)(Ar)N]Si (A), (L)[(1,5-C₈H₁₄)B(←:CNCy)(Ar)N]Si (A'), (L)[(1,5-C₈H₁₄)B(←:CNCy)-(Ar')N]Si (A″), and (L)[(1,5-C₈H₁₄)B(←:CN-2,6-Me₂C₆H₃)(Ar')N]Si (A‴) as the respective intermediates. The as-followed transition states TS, TS1', TS1″, and TS‴ all feature probable Si:→C(═N):→B bonding with different Gibbs energies of 7.24, 2.46, 3.86, and 6.59 kcal/mol, respectively, due to variation among the Ar, Ar', 2,6-Me₂C₆H₃, and Cy groups in these species, and reacted in different ways.