Catalytic Activity of Molybdenum Complexes Bearing PNP‐Type Pincer Ligand toward Ammonia Formation

Abstract

We newly designed and prepared a novel molybdenum complex bearing a 4‐[3,5‐bis(trifluoromethyl)phenyl]pyridine‐based PNP‐type pincer ligand, based on the bond dissociation free energies (BDFEs) of the N−H bonds in molybdenum‐imide complexes bearing various substituted pyridine‐based PNP‐type pincer ligands. The complex worked as an excellent catalyst toward ammonia formation from the reaction of an atmospheric pressure of dinitrogen with samarium diiodide as a reductant and water as a proton source under ambient reaction conditions, where up to 3580 equivalents of ammonia were formed based on the molybdenum atom of the catalyst. The catalytic activity was significantly improved by one order of magnitude larger than that observed when using the complex before modification.

Iron promoted end-on dinitrogen-bridging in heterobimetallic complexes of uranium and lanthanides

“…The use of Sm( ii ) as an electron source, under the form of a simple iodide salt or in more sophisticated coordination complexes, has led to some of the highest yields and efficiencies for the catalytic transformation of N 2 to NH 3 or N 2 H 4 over the last 10 years. 55–58…”

“…Besides the fundamental interest in dinitrogen reduction promoted by f-elements, which has resulted in the isolation of unusual N 2 3− species 52–54 and in rare examples of dinitrogen functionalization, 43 there is currently high interest in probing the interaction of lanthanides with iron based dinitrogen complexes because of the high efficiency of Ln( ii ) ions as electron sources in the catalytic conversion of N 2 to ammonia or hydrazine. 55–58 Here we isolated and characterized a range of rare end-on bridged dinitrogen complexes of uranium and lanthanides.…”

(Electro)chemical N2 Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand

“…The TON and TOF could be dramatically increased by using the proton-coupled electron transfer (PCET) reagents SmI 2 with alcohols or water and I Cl . Since the corresponding Mo­(IV) nitrido complex [ L PNP Mo­(N)­I] showed a similar catalytic performance than I I , the authors proposed later that the reaction with I I proceeds via N 2 splitting and subsequent reduction and protonation of the Mo nitrido complex. , In contrast to the earlier study, complexes with electron-withdrawing substituents in para position of the pyridine unit showed enhanced activity when using the Sm-based PCET reagents …”

“…9,10 In contrast to the earlier study, complexes with electron-withdrawing substituents in para position of the pyridine unit showed enhanced activity when using the Smbased PCET reagents. 11 The first molecular metal catalyst beyond molybdenum was reported by the group of Peters in 2013, who introduced an iron tris(phenylphosphino)borane complex, which is active in the nitrogen reduction reaction (N 2 RR). 12 In the following years, several more molecular N 2 -to-NH 3 catalysts were reported based on Co, Os, Ru, Ti, V, Cr, Mo, and Re ions.…”

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

“…Since then Nishibayashi and others have reported numerous other examples of pincer-ligated Mo catalysts, some of which yield extremely high turnovers, including systems that can utilize water as the proton source. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Very recently, it was reported that addition of an electron-withdrawing substituent at the para-position of the pyridine ring (Figure 1b) dramatically enhanced catalytic activity with the use of SmI2/H2O as the source of electrons and protons. 34 In general, most of these catalysts have the "PYP pincer" motif in which two terminal dialkyl-or diarylphosphino groups are connected to a neutral coordinating group such as the pyridine group of PNP, a central phosphino group, or an N-heterocyclic carbene group.…”