A series of chromium–halide, –nitride, and –dinitrogen com-plexes bearing a carbene- and phosphine-based PCP-type pin-cer ligand is newly prepared and some of them are found to work as effective catalysts to reduce dinitrogen under atmos-pheric pressure, whereby up to 8.40 equiv of ammonia and 2.46 equiv of hydrazine (13.32 equiv of fixed N atom) are produced based on the chromium atom. To the best of our knowledge, this is the first successful example of chromium-catalyzed conversion of dinitrogen to ammonia and hydrazine under mild reaction conditions.
Among synthetic models of nitrogenases, iron–dinitrogen complexes with a Fe–C bond have attracted increasing attention in recent years. Here we report the synthesis of square-planar iron(I)–dinitrogen complexes supported by anionic benzene-based PCP- and POCOP-type pincer ligands as carbon donors. These complexes catalyze the formation of ammonia and hydrazine from the reaction of dinitrogen (1 atm) with a reductant and a proton source at -78 °C, producing up to 252 equiv of ammonia and 68 equiv of hydrazine (388 equiv of fixed N atom) based on the iron atom of the catalyst. Anionic iron(0)–dinitrogen complexes, considered an essential reactive species in the catalytic reaction, are newly isolated from the reduction of the corresponding iron(I)–dinitrogen complexes. This study examines their reactivity using experiments and DFT calculations.
In the presence of a catalytic amount of a dinitrogen-bridged dirhenium complex bearing PNP-type pincer ligands, an atmospheric pressure of dinitrogen reacted with potassium as a reductant and dicyclohexylchloroborane as a borylating reagent at room temperature to give 14.4 equiv of ammonia and 3.2 equiv of hydrazine based on the rhenium atom of the catalyst upon hydrolysis (20.8 equiv of fixed N atom). This result demonstrates the first successful example of the borylation of dinitrogen into ammonia and hydrazine equivalents under ambient conditions with rhenium complexes as catalysts.
Molybdenum–carbamate complex bearing a pyridine-based 2,6-bis(di-tert-butylphosphinomethyl)pyridine (PNP)-pincer ligand is synthesised from the reaction of a molybdenum–nitride complex with phenyl chloroformate. The conversion between the molybdenum–carbamate complex and the molybdenum–nitride complex under ambient reaction conditions is achieved. The use of samarium diiodide (SmI2) as a reductant promotes the formation of cyanate anion (NCO−) from the molybdenum–carbamate complex as a key step. Based on the stoichiometric reactions, we have demonstrated a synthetic cycle for NCO− from dinitrogen mediated by the molybdenum–PNP complexes in two steps. Based on this synthetic cycle, we have achieved the catalytic synthesis of NCO− from dinitrogen under ambient reaction conditions. We believe that these results described in this manuscript provide valuable information to achieve the catalytic transformations of dinitrogen into valuable organonitrogen compounds under ambient reaction conditions.
Herein, we established an iridium- and molybdenum-catalysed process for the synthesis of ammonia from dinitrogen that takes place under ambient reaction conditions and under visible light irradiation. In this reaction system, cationic iridium complexes bearing 2-(2-pyridyl)phenyl and 2,2’-bipyridine-type ligands and molybdenum triiodide complexes bearing N-heterocyclic carbene-based PCP-type pincer ligands acted as cooperative catalysts to activate 9,10-dihydroacridine and dinitrogen, respectively. Interestingly, under visible light irradiation, 9,10-dihydroacridine acted as a one-electron and one-proton source. The findings of this study provide a novel approach to catalytic nitrogen fixation that is driven by visible light energy. The reaction of dinitrogen with 9,10-dihydroacridine was not thermodynamically favoured, and it only took place under visible light irradiation. Therefore, the described reaction system is one that affords visible light energy–driven ammonia formation from dinitrogen. The findings reported herein can contribute to the development of novel next-generation nitrogen fixation systems powered by renewable energy.
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