Lithium-Assisted Dinitrogen Reduction Mediated by NbLiNO Cluster Anions: Electron Donors or Structural Units.

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 NbLiNO have been synthesized and reacted with N at room temperature. The detailed experimental and theoretical investigations indicate that NbLiNO is capable to cleave the N≡N bond and the Li atoms in NbLiNO act as electron donors in the N reduction reaction. With the increase in the number of oxygen atoms, the reactivity toward N is reduced from adsorption via a side-on end-on mode in NbLiNO to the inertness of NbLiNO. In NbLiNO 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.