A Bis(silylene)-Substituted ortho-Carborane as a Superior Ligand in the Nickel-Catalyzed Amination of Arenes

摘要

The synthesis and structure of the first 1,2-bis(NHSi)-substituted ortho-carborane [(LSi:)C](2)B10H10 (termed SiCCSi) is reported (NHSi=N-heterocyclic silylene; L=PhC(NtBu)(2)). Its suitability to serve as a reliable bis(silylene) chelating ligand for transition metals is demonstrated by the formation of [SiCCSi]NiBr2 and [SiCCSi]Ni(CO)(2) complexes. The CO stretching vibration modes of the latter indicate that the Si-II atoms in the SiCCSi ligand are even stronger sigma donors than the P-III atoms in phosphines and C-II atoms in N-heterocyclic carbene (NHC) ligands. Moreover, the strong donor character of the [SiCCSi] ligand enables [SiCCSi]NiBr2 to act as an outstanding precatalyst (0.5mol% loading) in the catalytic aminations of arenes, surpassing the activity of previously known molecular Ni-based precatalysts (1-10mol%).