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.