Reactions of gas-phase species with small molecules are being actively studied to understand the elementary steps and mechanistic details of related condensed-phase processes. Activation of the very inert N≡N triple bond of dinitrogen molecule by isolated gas-phase species has attracted considerable interest in the past few decades. Apart from molecular adsorption and dissociative adsorption, interesting processes such as C-N coupling and degenerate ligand exchange were discovered. The present review focuses on the recent progress on adsorption, activation, and functionalization of N2 by gas-phase species (particularly metal cluster ions) using mass spectrometry, infrared photo-dissociation spectroscopy, anion photoelectron spectroscopy, and quantum chemical calculations including density functional theory and high-level ab initio calculations. Recent advances including characterization of adsorption products, dependence of clusters’ reactivity on their sizes and structures, and mechanisms of N≡N weakening and splitting have been emphasized and prospects have been discussed.

Nitrogen (N 2 ) fixation is a challenging and vital issue in chemistry. Inspired by the fact that the active sites of nitrogenases are polynuclear metal sulfide clusters, the reactivity of gas-phase metal sulfide clusters toward N 2 has received considerable attention to gain fundamental insights into nitrogen fixation. Herein, neutral tantalum sulfide clusters have been prepared and their reactivity toward N 2 has been investigated by mass spectrometry in conjunction with density functional theory (DFT) calculations. The experimental results showed that Ta 3 S n (n = 0−3) could adsorb N 2 , while Ta 3 S 4 was inert to N 2. The DFT calculations revealed that the complete cleavage of the NN bond on the trinuclear metal center in the Ta 3 S 0−3 /N 2 reaction systems was overall barrierless under thermal collision conditions. The sulfur ligands can facilitate the approaching of N 2 toward the metal center but weaken the electron-donating ability of the metal center. The inertness of Ta 3 S 4 is ascribed to the electron-deficient state of Ta 3 in Ta 3 S 4 and the least effective orbital interaction in the Ta 3 S 4 /N 2 couple. This study provides new insights into the ligand effect on the interaction of the metal clusters with N 2.

Inspired by the fact that the active centers of natural nitrogenases are polynuclear iron−sulfur clusters, the reactivity of isolated iron−sulfur clusters toward N 2 has received considerable attention to gain fundamental insights into the activation of the NN triple bond. Herein, a series of gasphase iron−sulfur cluster anions Fe x S y − (x = 1−8, y = 0−x) were prepared and their reactivities toward N 2 were investigated systematically by mass spectrometry. Among the 44 investigated clusters, only Fe 5 S 2 − and Fe 5 S 3 −