Catalytic Reduction of Dinitrogen to Ammonia at a Single Molybdenum Center

Abstract

Since our discovery of the catalytic reduction of dinitrogen to ammonia at a single molybdenum center, we have embarked on a variety of studies designed to further understand this complex reaction cycle. These include studies of both individual reaction steps and of ligand variations. An important step in the reaction sequence is exchange of ammonia for dinitrogen in neutral molybdenum(III) compounds. We have found that this exchange reaction is first order in dinitrogen and relatively fast (complete in <1 h) at 1 atm of dinitrogen. Variations of the terphenyl substituents in the triamidoamine ligand demonstrate that the original ligand is not unique in its ability to yield successful catalysts. However, complexes that contain sterically less demanding ligands fail to catalyze formation of ammonia from dinitrogen; it is proposed as a consequence of a base-catalyzed decomposition of a diazenido (Mo-NANH) intermediate.

Synthesis of Fuels and Value-Added Nitrogen-Containing Compounds from N2

“…Vanadium and molybdenum were of particular interest due to their terrestrial abundance and well-established role in both biological and transition metal catalyzed nitrogen fixation. The independent reports by Schrock 6 and Nishibayashi 7 of catalytic ammonia synthesis with welldefined molybdenum coordination complexes as pre-catalysts inspired our hypothesis ( Figure 1). We note that catalytic N 2 reduction was only achieved when lutidinium salts were combined with outer sphere reductants such as (η 5 -C 5 Me 5 ) 2 Cr and (η 5 -C 5 H 5 ) 2 Co.…”

Synthesis of [(HIPTNCH2CH2)3N]V Compounds (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) and an Evaluation of Vanadium for the Reduction of Dinitrogen to Ammonia

“…This solid was again dried at room temperature in vacuo to minimum pressure to yield the lime green product (4.6 g, 86 %). Substituting (TMS) 2 NK for (TMS) 2 NLi gave the same product (2. were added to a 20 mL scintillation vial along with a glass-coated stir-bar and 5 -10 mL of solvent (typically THF, but also DME, ether, benzene, or toluene). Using ethereal solvents, the solution turns red within minutes (overnight in the case of toluene or benzene) and was filtered through glass wool in a pipet to remove the graphite and excess KC 8 .…”

Die katalytische Reduktion von Distickstoff zu Ammoniak mit Molybdän: Theorie und Experiment

“…[31,32] Wir wendeten uns dann Molybdänkomplexen mit dem [HIPTN 3 N] 3À -Liganden zu (HIPT = 3,5-(2,4,6-iPr 3 C 6 H 2 ) 2 C 6 H 3 , Hexaisopropylterphenyl; Schema 1), [33,34] Für eine hypothetische "lineare" Reduktion von N 2 wurden Intermediate vorgeschlagen (Schema 2), von denen die folgenden acht synthetisiert und kristallographisch und mit anderen Verfahren charakterisiert wurden: [33][34][35][36] 3À leicht modifiziert waren, [40,41] und neuere Befunde bei der Reduktion von Distickstoff zusammengefasst. [42][43][44] Die eingesetzte Säure beeinflusst den Erfolg der Reduktion sehr stark. [42] Auch mit einem schwächeren Reduktionsmittel (CoCp 2 ) verläuft die Reaktion noch katalytisch, die Ausbeute an Ammoniak ist dann aber nur etwa halb so groß.…”