Cleavage and Formation of Molecular Dinitrogen in a Single System Assisted by Molybdenum Complexes Bearing Ferrocenyldiphosphine

Abstract

The NN bond of molecular dinitrogen bridging two molybdenum atoms in the pentamethylcyclopentadienyl molybdenum complexes that bear ferrocenyldiphosphine as an auxiliary ligand is homolytically cleaved under visible light irradiation at room temperature to afford two molar molybdenum nitride complexes. Conversely, the bridging molecular dinitrogen is reformed by the oxidation of the molybdenum nitride complex at room temperature. This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli using a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine under ambient conditions.Nitrogen fixation, the production of ammonia from molecular dinitrogen, is one of the most important chemical processes on earth because ammonia is widely used as an essential source of nitrogen fertilizers. Industrially, ammonia is produced from molecular dinitrogen and molecular dihydrogen using iron-based heterogeneous catalysts under harsh reaction conditions, such as quite high temperatures and pressures. [1] In the Haber-Bosch process, the rate-determining step is the dissociative chemisorption of dinitrogen on the surface of the iron catalyst, which includes adsorption of dinitrogen, cleavage of the NN triple bond, and the bonding of two nitrogen atoms to the iron surface as nitride species. [1] Although all these elementary steps are known to occur reversibly, it is still quite difficult to understand the heterogeneous reaction in detail on the atomic and molecular levels.Since the first discovery of a transition-metal-dinitrogen complex, [2] various stoichiometric and catalytic transformations using transition-metal-dinitrogen complexes have been well investigated toward the development of the next generation nitrogen fixation system. [3,4] During our study on the development of novel nitrogen fixation system under mild reaction conditions, [4b, 5] we have focused on use of ferrocenyldiphosphine as an auxiliary ligand chelating to molybdenum atom to capture and activate molecular dinitrogen. [6] We have now found that molecular dinitrogen is cleaved and reformed on the pentamethylcyclopentadienyl molybdenum complexes in medium oxidation states bearing ferrocenyldiphosphine as an auxiliary ligand. In this reaction system, molecular dinitrogen bridging two molybdenum moieties is cleaved under visible light irradiation at room temperature to afford the corresponding molybdenum nitride complex. Conversely, the bridging molecular dinitrogen is reformed by oxidation of the molybdenum nitride complex at room temperature. This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli (both photochemically and oxidatively) using a single system under ambient conditions.When the monocationic dinitrogen-bridged dimolybdenum complex chelated by 1,1'-bis(diethylphosphino)ferrocene (depf) [6a] (1), which was prepared by the reaction of molybdenum(II)-di...

Mechanism of Chemical and Electrochemical N2 Splitting by a Rhenium Pincer Complex

“… 13 , 48 , 49 These simple considerations are showcased by Cummins’ S 6 -symmetric intermediate [{( t BuArN) 3 Mo} 2 (N 2 )] 12 , 50 ( Scheme 7 ) and other examples. 18 , 51 The electronic structure computations for 3 are in full agreement with this picture ( Figure 9 ). In the current case, the square-pyramidal ligand field renders nonbonding, metal d-orbital based MOs with δ-symmetry ( Figure 9 , MO238/239) energetically accessible to host the four additional valence electrons in the dirhenium complex, i.e., {ReN 2 Re} 4+ (π 10 δ 4 ) vs {MoN 2 Mo} 6+ (π 10 ) ( Scheme 7 ).…”

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

“…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.…”

Catalytic Dinitrogen Fixation to Form Ammonia at Ambient Reaction Conditions Using Transition Metal-Dinitrogen Complexes

“…Photochemical cleavage of the dinitrogen ligand bridging two transition‐metal species to afford nitrido complexes has also been reported for some molybdenum, tungsten, and osmium complexes 66, 67. Our group has recently found that the N≡N triple bond of the dinitrogen ligand bridging two molybdenum moieties in the neutral dinitrogen‐bridged dimolybdenum complex bearing 1,1′‐bis(diethylphosphino)ferrocene (depf) as an auxiliary ligand was homolytically cleaved under visible light irradiation at room temperature to give two equiv.…”

“…Conversely, the bridging molecular dinitrogen was reformed to afford the dicationic dinitrogen‐bridged dimolybdenum when the nitrido complex was oxidized by an equimolar amount of ferrocenium tetrakis[3,5‐bis(trifluoromethyl)phenylborate] ( ) at room temperature. The neutral dinitrogen‐bridged dimolybdenum complex and the dicationic dinitrogen‐bridged dimolybdenum complex, prepared via one‐electron reduction by potassium graphite (KC 8 ) or one‐electron oxidation by from the monocationic dinitrogen‐bridged dimolybdenum complex, respectively, could be converted into one another (Scheme ) 66, 68. Thus, the molybdenum moieties bearing ferrocenyldiphosphine were shown to assist the novel process where the cleavage and reformation of molecular dinitrogen are induced by a pair of two different external stimuli (photochemistry and redox) under ambient reaction conditions 66, 69…”

“…also worked, but as less effective catalysts under the same reaction conditions 116. The anionic dinitrogen‐bridged molybdenum‐dinitrogen complex, bearing only one ferrocenyldiphosphine ligand [Cp*Mo(μ‐N 2 ){Na(15‐crown‐5)}(depf)], also works, but less effectively, as a catalyst towards the formation of N(SiMe 3 ) 3 (Scheme ) 66. These results suggest that the existence of ferrocenyl moieties plays some important part in the efficient activation of catalysis.…”