Eta3-sandwich-like complexes based on the smallest polynitrogen ring.

Over the past decades, polynitrogen chemistry has witnessed rapidly growing progress. Unfortunately and to our great surprise, eta(3)-assembled species based on the simplest polynitrogen ring (N(3)) have never been reported. In this paper, we report the first successful assembly design of the long-escaped N(3)-based compounds, that is, N(3)NiN(3), N(3)M(CO)(2)N(3) ((M,q), = (Fe,0) (Mn,-1)), N(3)M(CO)(3) ((M,q) = (Co,0), (Fe,-1)), and N(3)MCp ((M,q) = (Ni, 0), (Co,-1)), at the density functional level. The conversion and dissociation of them need to overcome considerable barriers kinetically. To our surprise, the detailed structural, charge distribution, and orbital analyses consistently reveal a triplet polynitrogen unit, cyclic-(3)N(3)(-), rather than another simplest trinitrogen unit cyclic-(1)N(3)(+). The two unpaired spins within the naked cyclic-(3)N(3)(-) have effectively participated in the bonding interaction with the central transition-metal atoms (here, M is Ni, Fe, Co, and Mn). Moreover, the possible experimental routes of N(3)Co(CO)(3) were proposed. The diradical-like polynitrogen ring, cyclic-(3)N(3)(-), would add to the polynitrogen family as a novel building block. The assembly-designed species await future experimental verification.