Abstract
An unprecedented, spontaneous, and complete cleavage of the triple bond of N(2) in the thermal reaction of (15)N(2) with Ta(2)(14)N(+) 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 N(2), mediated by Ta(2)N(+), constitutes a full catalytic cycle. A frontier orbital analysis reveals that the scission of the N(2) triple bond is essentially governed by the donation of d-electrons from the 2 metal centers into antibonding π*-orbitals of N(2) and by the concurrent migration of electrons from bonding π- and σ-orbitals of N(2) 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.