Lithium-Assisted Dinitrogen Reduction Mediated by Nb₂LiNO_1–4^– Cluster Anions: Electron Donors or Structural Units

Abstract

Alkali atoms are usually used as promoters to significantly increase the catalytic activity of transition-metal catalysts in a wide range of reactions such as dinitrogen conversion reactions. However, the role of alkali metal atoms remains controversial. Herein, a series of quaternary cluster anions containing lithium atoms Nb 2 LiNO 1−4 − have been synthesized and reacted with N 2 at room temperature. The detailed experimental and theoretical investigations indicate that Nb 2 LiNO − is capable to cleave the NN bond and the Li atoms in Nb 2 LiNO 1,2 − act as electron donors in the N 2 reduction reaction. With the increase in the number of oxygen atoms, the reactivity toward N 2 is reduced from adsorption via a side-on end-on mode in Nb 2 LiNO 2 − to the inertness of Nb 2 LiNO 4 − . In Nb 2 LiNO 3,4 − anions, the Li atoms are bonded with oxygen atoms, acting as structural units to stabilize structures. Therefore, the roles of alkali atoms are able to change with different chemical environments of active sites. For the first time, we reveal how the number of ligands (oxygen atoms herein) can be used to finely regulate the reactivity toward N 2 .

Trimetallic clusters in the sumanene bowl for dinitrogen activation

“…30–32 Therefore, using a cluster model to study the activation of nitrogen is an effective method. So far, the reaction of metal-containing clusters with N 2 has been widely studied, 33–53 while only a few studies are based on trimetallic clusters, such as pure metals (Mo 2 M, where M = Li, Na, K, Mg, and Ca), 54 metal carbides (V 3 C 4 − , 55 V 3− x Ta x C 4 − , 56 and FeV 2 C 2 − 57 ), hydrides (Co 3 D n − , 58 Ta 3 N 3 H 0,1 − , 59 and Rh 3 D n − 60 ), nitrides (Sc 3 N + 61 and Nb 2 LiNO 1–4 − 62 ) and sulfides (Ta 3 S n , 63 Nb 3 S n , and W 3 S n 64 ). Trimetallic clusters provide more coordination modes for N 2 adsorption than monometallic and bimetallic clusters and allow nitrogen to be dissociated for example with the end-on: side-on: side-on (ESS) coordination mode, which can only be realized in trimetallic (or larger) clusters.…”

Dinitrogen Activation by Dihydrogen and Quaternary Cluster Anions AuNbBO–: Nb- and B-Mediated N2 Activation and Au-Assisted Nitrogen Transfer

“…The combination of experimental and computational methods for the study of “isolated” reactants in the gas phase provides an ideal venue for revealing the reaction mechanisms and kinetics at a molecular level. − Notably, both homo- and heteronuclear metal species can be produced in gas-phase experiments, and the reactions of these transition metal-based species with N 2 have been extensively studied. In the previously reported reactions, only a few metal-containing species, such as Sc 2 , Ta 2 + , Ta 2 C 4 – , Ta 2 N + , V 3 C 4 – , Ta 3 N 3 H 0,1 – , NbH 2 – , NbB 3 O 2 – , FeTaC 2 – , AuNbBO – , and Nb 2 LiNO – , can fully split NN bonds. Moreover, simultaneous activation of N 2 and H 2 to form NH or NH 2 units has been reported only in our previous work on Sc 3 N + /H 2 /N 2 systems .…”

“…Moreover, simultaneous activation of N 2 and H 2 to form NH or NH 2 units has been reported only in our previous work on Sc 3 N + /H 2 /N 2 systems . In addition, there have been few reports about the reactivity of quaternary cluster ions toward N 2 . , Considering that noble metals, such as Ru, are used in the ammonia catalysts and our observation that niobium atoms exhibit excellent reactivity in N 2 activation and transformation reactions, ,,, we designed and synthesized the quaternary heteronuclear metal anions AuNbBO – and studied the reactions with N 2 and H 2 experimentally and theoretically. The findings suggest that the AuNbBO – anion can subsequently activate N 2 and H 2 at room temperature and efficiently transfer two activated N atoms to form one imido (NH) unit and one NBO moiety.…”

“…29 In addition, there have been few reports about the reactivity of quaternary cluster ions toward N 2 . 27,28 Considering that noble metals, such as Ru, are used in the ammonia catalysts 10 and our observation that niobium atoms exhibit excellent reactivity in N 2 activation and transformation reactions, 24,25,27,28 we designed and synthesized the quaternary heteronuclear metal anions AuNbBO − and studied the reactions with N AuNbBO − anion can subsequently activate N 2 and H 2 at room temperature and efficiently transfer two activated N atoms to form one imido (NH) unit and one NBO moiety. Moreover, the other H atom can transfer to the newly formed NH unit, leading to a small number of amido (*NH 2 ) units.…”

Spectroscopic Characterization of the Synergistic Mechanism of Ruthenium–Lithium Hydrides for Dinitrogen Cleavage

“…Alkali and alkaline earth metals are electron-rich and have easy access to high-energy orbitals and the correct symmetry to interact effectively with the π* orbital of N 2 . Hence, they usually serve as the promoters for ammonia catalysts to increase the N 2 dissociation rate. − The alkali and alkaline earth hydrides (denoted as AMHs) feature a negatively charged hydrogen atom, which can be regarded as an electron and hydrogen carrier by abstracting and hydrogenating the dissociated N from the transition metals. The synergy between alkali or alkaline earth metal hydrides and transition metals allows both early and late 3d TM–AMH composites to exhibit superior mild-condition catalytic activities .…”