Theoretical investigation of borane compounds mimicking transition metals for N 2 fixation and activation.

N 2 fixation is very difficult because of the nonpolarity and high stability of N 2 . Traditionally, it is achieved by transition metal (TM) systems utilizing the back donation from the d orbitals of the TM to the antibonding π* orbitals of N 2 to activate N 2 . This back donation is rare for main group compounds due to the lack of high-lying valence d orbitals. In the present study, we show that borane compounds with weak B-X (X = H, Si, Ge, and Sb) bonds can mimic TM systems and be used to fix and activate N 2 . This is achieved by the back donation from the σ bonding orbitals of the B-X bonds to the antibonding π* and σ* orbitals of N 2 . There is even a linear relationship between the number of B-X bonds and the binding potential energy of N 2 with BR 1 R 2 R 3 (R 1 , R 2 , R 3 = H, CH 3 , SiH 3 , GeH 3 , and SbH 2 ). Based on these findings, we designed several stable silylborane compounds that are feasible for N 2 fixation and activation under mild reaction conditions, i.e. , room temperature and 1 atm. In some sandwich-like complexes formed between N 2 and silylborane compounds, N 2 is even activated from the triple bond to double bond.