Preparation and Reactivity of Rhenium–Nitride Complexes Bearing PNP-Type Pincer Ligands toward Nitrogen Fixation

A series of mononuclear rhenium­(V)–nitride complexes bearing substituted pyridine-based PNP-type pincer ligands are synthesized. The substituent in the PNP-type pincer ligand does not significantly improve the catalytic activity for ammonia formation, while the introduction of a methoxy group increases the catalytic activity for the silylamine formation. Stoichiometric studies reveal that a rhenium­(V)–nitride complex bearing a nonsubstituted PNP-type pincer ligand is transformed into a dearomatized rhenium­(V)–nitride dimer under reductive conditions, while the dearomatized rhenium­(V)–nitride dimer exhibits catalytic activity for the nitrogen fixation reactions. However, a rhenium­(V)–nitride complex bearing a methyl-substituted PNP-type pincer ligand shows different reactivity by reduction, where deprotonation of the methylene group of the PNP-type pincer ligand is observed.