n– (n = 1–4) with Dinitrogen]]>

摘要

Dinitrogen activation/fixation is one of the most important and challenging subjects in synthetic as well as theoretical chemistry. In this study, the adsorption reactions of N_(2) onto TaC_(n )~(–) (n = 1–4) cluster anions have been investigated by means of mass spectrometry in conjunction with density functional theory calculations. Following the experimental results that only TaC_(4)~(–) was observed to adsorb N_(2), theoretical calculations predicted that the TaC_(4)~(–) reaction system (TaC_(4)~(–) + N_(2) → TaC_(4)N_(2)~(–)) has a negligible barrier on the approach of N_(2) molecule while insurmountable barriers are located on the reaction pathways of TaC_(1–3)~(–)/N_(2) reaction systems. The natural bond orbital and molecular orbital analysis indicated that the more positive charge on the metal center of TaC_(1–4)~(–) would facilitate the initial approach of the nonpolar N_(2) molecule, and the appropriate frontier orbital of TaC_(1–4)~(–) with proper symmetry (π-type 5d orbital) which can match up well with the π* antibonding orbital of the N_(2) molecule with less σ repulsion and more possibility for π back-donation would be helpful for the formation of the stable encounter complexes. This study reveals the fundamental rules and key factors governing the N_(2) adsorption.