Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN3PMo(V) Nitride Complex: Significant Enhancement via Ligand Post-Modification

Abstract

Efforts to develop organometallic complexes for catalytic nitrogen reduction have seen significant progress in recent years. However, the strategies for improving the activity of the homogenous catalysts have been mainly focused on alternating ligands and metals so far. Herein, we report that the activity and stability of a PN3P-Mo pincer complex ( 2) toward dinitrogen (N2) reduction were greatly enhanced through the post-modification of the PN3P pincer framework of its parent complex ( 1). A high ratio of NH3/Mo (3525) was achieved in the presence of SmI2 as a reductant. In sharp contrast, 1 only afforded an NH3/Mo ratio of 21. Moreover, since supported by the anionic pincer ligand, 2 furnished a high oxidation state Mo(V) nitride complex as a plausible key intermediate in the catalytic process via N2-cleavage, suggesting a catalytic cycle that may involve different oxidation states (II/V) from those with 10-π electron configuration in the literature.