Practical Ligand-Enabled N₂Adsorption of Rhenium(I) Carbonyl Complexes Based on Meridionally Coordinated Terpyridine

The prerequisite for N₂activation under mild conditions is the efficient adsorption of N₂onto metal sites. Understanding the selectivity and environmental dependence of N₂adsorption is essential for elucidating fundamental mechanisms and designing efficient catalysts. In this study, we synthesized the complex mer, cis-Re(tpy-κ³N)(CO)₂Cl (where tpy stands for terpyridine) and investigated its reactivity toward N₂using electrospray ionization mass spectrometry (ESI-MS) and density functional theory (DFT) calculations. Using ESI, the species [Re(tpy)]⁺, [Re(tpy)(CO)]⁺and [Re(tpy)(CO)₂]⁺were generated and subsequently allowed to react with N₂. The mass spectrometry experiments revealed the reactivity order of N₂adsorption as: [Re(tpy)]⁺> [Re(tpy)(CO)]⁺≫ [Re(tpy)(CO)₂]⁺(inert). DFT calculations indicate the presence of π back-donation between the Re atom and N₂. The observed decrease in reactivity can be attributed to two primary factors: (i) electron depletion at the Re center by CO ligands, which diminishes its π back-donation capacity, and (ii) steric hindrance from CO ligands, which hinders N₂access to the preferred planar coordination site. This work provides key insights into the synergistic effects between organic ligands and transition metals, advancing the rational design of molecular systems for N₂adsorption and activation.