Complete cleavage of the N≡N triple bond by Ta<sub>2</sub>N<sup>+</sup> via degenerate ligand exchange at ambient temperature: A perfect catalytic cycle.

Geng, Caiyun; Li, Jilai; Weiske, Thomas; Schwarz, Helmut · Proc Natl Acad Sci U S A · 2019

basic_science · Level V

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Abstract

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