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

Two borylaminoamidinatosilylenes (L)[(1,5-C 8 H 14 )B(Ar)N]Si (L = PhC(NtBu) 2 , Ar = 2,6- i Pr 2 C 6 H 3 ( 1 )) and (L)[(1,5-C 8 H 14 )B(Ar')N]Si (Ar' = 2,4,6-Me 3 C 6 H 2 ( 2 )) have been prepared and utilized to investigate the reaction toward isocyanide. Reactions of 1 with the respective CN-2,6-Me 2 C 6 H 3 and CNCy (Cy = cyclo -C 6 H 11 ) produced compounds (L)Si(NAr)C(N-2,6-Me 2 C 6 H 3 )B(1,5-C 8 H 14 )(CN-2,6-Me 2 C 6 H 3 ) ( 3 ) and (L)Si(NAr)C(NCy)C(NCy)B(1,5-C 8 H 14 )(CNCy) ( 4 ). Reactions of 2 with the respective CNCy and CN-2,6-Me 2 C 6 H 3 yielded compounds cyclo -(L)SiN(Ar')C(NCy)B(1,5-C 8 H 14 )C(NCy) ( 5 ) and cyclo -(L)[(1,5-C 8 H 14 )B(Ar')N]SiC(CN-2,6-Me 2 C 6 H 3 )N(2,6-Me 2 C 6 H 3 )C(N-2,6-Me 2 C 6 H 3 ) ( 6 ). Compounds 3 - 6 have different compositions and structures from each other. Density functional theory (DFT) calculations suggest initial formation of (L)[(1,5-C 8 H 14 )B(←:CN-2,6-Me 2 C 6 H 3 )(Ar)N]Si ( A ), (L)[(1,5-C 8 H 14 )B(←:CNCy)(Ar)N]Si ( A '), (L)[(1,5-C 8 H 14 )B(←:CNCy)-(Ar')N]Si ( A ″), and (L)[(1,5-C 8 H 14 )B(←:CN-2,6-Me 2 C 6 H 3 )(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-Me 2 C 6 H 3 , and Cy groups in these species, and reacted in different ways.