Complete cleavage of the N≡N triple bond by Ta2N+ via degenerate ligand exchange at ambient temperature: A perfect catalytic cycle.

An unprecedented, spontaneous, and complete cleavage of the triple bond of N2 in the thermal reaction of 15N2 with Ta2 14N+ was observed experimentally by Fourier transform ion cyclotron resonance mass spectrometry; mechanistic aspects of the degenerate ligand exchange were addressed by high-level quantum chemical calculations. The "hidden" dis- and reassembly of N2, mediated by Ta2N+, constitutes a full catalytic cycle. A frontier orbital analysis reveals that the scission of the N2 triple bond is essentially governed by the donation of d-electrons from the 2 metal centers into antibonding π*-orbitals of N2 and by the concurrent migration of electrons from bonding π- and σ-orbitals of N2 into empty d-orbitals of the metals. This work may contribute to a rational design of catalysts in order to reduce the still enormous energy demand required for an artificial dinitrogen activation.