Dinitrogen Fixation and Reduction by Ta_3N_3H_(0,1)‐Cluster Anions at Room Temperature: Hydrogen-Assisted Enhancement of Reactivity

摘要

Dinitrogen activation and reduction is one of the most challenging and important subjects in chemistry. Herein, we report the N-2 binding and reduction at the well-defined Ta3N3H- and Ta3N3- gas-phase clusters by using mass spectrometry (MS), anion photoelectron spectroscopy (PES), and quantum-chemical calculations. The PES and calculation results show clear evidence that N-2 can be adsorbed and completely activated by Ta3N3H- and Ta3N3- clusters, yielding to the products Ta3N5H- and Ta3N5-, but the reactivity of Ta3N3H- is five times higher than that of the dehydrogenated Ta3N3- clusters. The detailed mechanistic investigations further indicate that a dissociative mechanism dominates the N-2 activation reactions mediated by Ta3N3H- and Ta3N3-; two and three Ta atoms are active sites and also electron donors for the N-2 reduction, respectively. Although the hydrogen atom in Ta3N3H- is not directly involved in the reaction, its very presence modifies the charge distribution and the geometry of Ta3N3H-, which is crucial to increase the reactivity. The mechanisms revealed in this gas-phase study stress the fundamental rules for N-2 activation and the important role of transition metals as active sites as well as the new significant role of metal hydride bonds in the process of N-2 reduction, which provides molecular-level insights into the rational design of tantalum nitride-based catalysts for N-2 fixation and activation or NH3 synthesis.