Catalytic Formation of Ammonia from Molecular Dinitrogen by Use of Dinitrogen-Bridged Dimolybdenum–Dinitrogen Complexes Bearing PNP-Pincer Ligands: Remarkable Effect of Substituent at PNP-Pincer Ligand

Abstract

A series of dinitrogen-bridged dimolybdenum-dinitrogen complexes bearing 4-substituted PNP-pincer ligands are synthesized by the reduction of the corresponding molybdenum trichloride complexes under 1 atm of molecular dinitrogen. In accordance with a theoretical study, the catalytic activity is enhanced by the introduction of an electron-donating group to the pyridine ring of PNP-pincer ligand, and the complex bearing 4-methoxy-substituted PNP-pincer ligands is found to work as the most effective catalyst, where 52 equiv of ammonia are produced based on the catalyst (26 equiv of ammonia based on each molybdenum atom of the catalyst), together with molecular dihydrogen as a side-product. Time profiles for the catalytic reactions indicate that the rates of the formation of ammonia and molecular dihydrogen depend on the nature of the substituent on the PNP-pincer ligand of the complexes. The formation of ammonia and molecular dihydrogen is complementary in the reaction system.

Nitrogenase-mimic iron-containing chalcogels for photochemical reduction of dinitrogen to ammonia

“…The 1 H NMR results shown in Fig. 4B demonstrate that both triplets and doublets could be observed, which correspond to 14 + doublets with irradiation time provides conclusive evidence that the detected ammonia originates from nitrogen gas.…”

“…To this end, inspired by the molecular structure and function of FeMoco, a number of groups have synthesized transition metal-dinitrogen complexes and examined stoichiometric transformations of their coordinated N 2 into NH 3 and N 2 H 4 (9-19). However, the operation of homogeneous transition metal-dinitrogen complexes usually requires organic solvents, strong reducing agents, and often extremely low operation temperatures (5,10,12,14). The prospect of using solar light energy to convert N 2 to ammonia is highly attractive but it represents a great challenge and is a less-investigated line of inquiry.…”

Recent Progress in Transition-Metal-Catalyzed Reduction of Molecular Dinitrogen under Ambient Reaction Conditions

“…Then, we investigated the catalytic nitrogen fixation using newly prepared complexes as catalysts (Scheme 14). 25 In reactions using 22 and 23 as catalysts, 21 equiv and 23 equiv of ammonia were produced based on the catalysts, respectively. When 24 and 25 were used as catalysts, larger amounts (28 equiv and 31 equiv) of ammonia were obtained based on the catalysts, respectively.…”

Exploring secondary-sphere interactions in Fe–NxHycomplexes relevant to N2fixation

“…While there has been considerable effort invested in the development of functional inorganic Mo and Fe systems as limiting models of biological nitrogen fixation, 10,11 there has been correspondingly less investment of effort towards incorporating secondary sphere interactions into such models. There are nonetheless several studies that have probed for secondary sphere interactions in M–N x H y species (Fig.…”