Facile conversion of ammonia to a nitride in a rhenium system that cleaves dinitrogen.

Rhenium complexes with aliphatic PNP pincer ligands have been shown to be capable of reductive N splitting to nitride complexes. However, the conversion of the resulting nitride to ammonia has not been observed. Here, the thermodynamics and mechanism of the hypothetical N-H bond forming steps are evaluated through the reverse reaction, conversion of ammonia to the nitride complex.

Dinitrogen Reduction to Ammonium at Rhenium Utilizing Light and Proton-Coupled Electron Transfer.

The direct scission of the triple bond of dinitrogen (N) by a metal complex is an alluring entry point into the transformation of N to ammonia (NH) in molecular catalysis. Reported herein is a pincer-ligated rhenium system that reduces N to NH via a well-defined reaction sequence involving reductive formation of a bridging N complex, photolytic N splitting, and proton-coupled electron transfer (PCET) reduction of the metal-nitride bond. The new complex (PONOP)ReCl (PONOP = 2,6-bis(diisopropylphosphinito)pyridine) is reduced under N to afford the -isomer of the bimetallic complex [(PONOP)ReCl](μ-N) as an isolable kinetic product that isomerizes sequentially upon heating into the and isomers.

Chemical Oxidation of a Coordinated PNP-Pincer Ligand Forms Unexpected Re-Nitroxide Complexes with Reversal of Nitride Reactivity.

Because of the thermodynamic demands of N cleavage, N-derived nitride complexes are often unreactive. The development of multistep N functionalization reactions hinges on methods for modulating nitride reactivity with supporting ligands. Here, we describe the reactions of N-derived Re-nitride complexes, including the first Re nitrides supported by a nitroxide-containing pincer ligand, and unusual examples of Re-nitride complexes.

Protonation and electrochemical reduction of rhodium- and iridium-dinitrogen complexes in organic solution.

Protonation and reduction of pincer-ligated Rh- and Ir-N complexes have been studied by NMR spectroscopy and cyclic voltammetry to assess the capability of these complexes to activate or reduce N. Protonation, which is a prerequisite to electrochemical reduction, results in a cationic metal-hydride that loses N under an atmosphere of Ar. Reduction of the metal-hydride results in fast disproportionation of an unobserved transient Ir species.

Coordination chemistry insights into the role of alkali metal promoters in dinitrogen reduction.

The Haber-Bosch process is a major contributor to fixed nitrogen that supports the world's nutritional needs and is one of the largest-scale industrial processes known. It has also served as a testing ground for chemists' understanding of surface chemistry. Thus, it is significant that the most thoroughly developed catalysts for N reduction use potassium as an electronic promoter.