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.