In silico activation of dinitrogen with a light atom molecule

The N N triple bond can be cleaved in silico with a Eight atom molecule containing only the earth abundant elements C, H, Si, and P. Extensive density functional theory (DFT) computations on various classes of peri-substituted scaffolds containing Lewis acidic and basic sites in the framework of frustrated Lewis pairs (FLP) indicate that the presence of two silyl cations and two P atoms in a flexible but not too flexible arrangement is essential for energy efficient N-2-activation. The non-bonding lone-pair electrons of the P atoms thereby serve as donors towards N-2, whereas the lone-pairs of N-2 donate into the silyl cations. Newly formed lone-pair basins in the N-2-adducts balance surplus charge. Thereby, the N - N bond distance is increased by astonishing 0.3 angstrom, from 1.1 angstrom in N-2 gas to 1.4 angstrom in the adduct, which makes this bond prone to subsequent addition of hydride ions and protonation, forming two secondary amine sites in the process and eventually breaking the N N triple bond. Potential formation of dead-end states, in which the dications (active states) aversively form a Lewis acid (LA)-Lewis base (LB) bond, or in which the LA and LB sites are too far away from each other to be able to capture N-2, are problematic but might be circumvented by proper choice of spacer molecules, such as acenaphtha-lene or biphenylene, and the ligands attached to the LA and LB atoms, such as phenyl or mesityl, and by purging the reaction solutions with gaseous N-2 in the initial reaction steps. Charge redistributions via N-2-activation and splitting were monitored by a variety of real-space bonding indicators (RSBIs) derived from the calculated electron and electron pair densities, which provided valuable insight into the bonding situation within the different reaction steps.

Automated summary

The N N triple bond can be cleaved in silico with a molecule containing C, H, Si, and P. The presence of two silyl cations and two P atoms in a flexible arrangement is essential for energy efficient N-2-activation. The non-bonding lone-pair electrons of the P atoms serve as donors towards N-2, whereas the lone-pairs of N-2 donate into the silyl cations. The N - N bond distance is increased in the adduct, making it prone to subsequent addition and breaking of the triple bond.