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-iPr(2)C(6)H(3) (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)[(1,5C8H14)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.

Automated summary

Two borylaminoamidinatosilylenes were synthesized and their reactions towards isocyanides were investigated. The structures, compositions, and reaction mechanisms of the resulting compounds were determined through experiments and calculations.