Catalytic Recycling of a Th–H Bond via Single or Double Hydroboration of Inactivated Imines or Nitriles

The catalytic activity of the metallacycle thorium amide [(Me3Si)2N]2Th­[κ2–(N,C)–CH2Si­(CH3)2N­(SiMe3)] (Th1) is presented for the selective dihydroboration of nitriles (CN) with pinacolborane (HBpin). Using significantly low catalyst loading (0.1 mol %), the dihydroborated amines were achieved by the hydroboration of the CN triple bond attached with aromatic, aliphatic, and heteroatom backbones with high turnover frequency (TOF) as compared to all the reported homogeneous metal catalysts in this reaction. In addition, for aldimines (CN), the hydroboration precatalyst Th2 has been synthesized by the protonolysis of a seven-membered N-heterocyclic iminato ligand (LH) and Th1. The Th2 crystal structure and its performance in the synthesis of hydroborated secondary amine are also here presented. Detailed kinetic studies and thermodynamic and stoichiometric experiments provided us with cumulative evidence supporting the proposed mechanism for the aforementioned reactions.