The classification of π-/σ-aromaticity depends on the electrons with the dominating contributions. Traditionally, π- and σ-aromaticity are used to describe the unsaturated and saturated systems, respectively. Thus, it is rarely reported that π-aromaticity is dominated in a saturated system. Here we demonstrate that π-aromaticity could be dominating in several fully saturated four-membered rings (4MRs), supported by various aromaticity indices including ΔBL, NICS, EDDB, MCI, and AdNDP.

Dinitrogen activation under mild conditions is important but extremely challenging due to the inert nature of the N-N triple bond evidenced by high bond dissociation energy (945 kJ/mol) and large HOMO-LUMO gap (10.8 eV). In comparison with largely developed transition metal systems, the reported main group species on dinitrogen activation are rare. Here, we carry out density functional theory calculations on methyleneboranes to understand the reaction mechanisms of their dinitrogen activation.

The σ-bond activation by main group element has received enormous attention from theoretical and experimental chemists. Here, the reaction of C-X (X = Cl, Br, I) bonds in benzyl and allyl halides with a pincer-type phosphorus(III) species was reported. A series of structurally robust phosphorus(V) compounds were formed via the formal oxidative addition reactions of C-X bonds to the phosphorus(III) center. Density functional theory calculations show that the nucleophilic addition process is more favorable than the direct oxidative addition mechanism.