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

Abstract

Red-black [HIPTN3N]Cr (1) ([HIPTN3N]3- = [(HIPTNCH2CH2)3N]3- where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3 = HexaIsoPropylTerphenyl) can be prepared from CrCl3, while green-black [HIPTN3N]Cr(THF) (2) can be prepared from CrCl3(THF)3. Reduction of {1|2} (which means either 1 or 2) with potassium graphite in ether at room temperature yields [HIPTN3N]CrK (3) as a yellow-orange powder. There is no evidence that dinitrogen is incorporated into 1, 2, or 3. Compounds that can be prepared readily from {1|2} include red [HIPTN3N]CrCO (4), blood-red [HIPTN3N]CrNO (6), and purple [HIPTN3N]CrCl (7, upon oxidation of {1|2} with AgCl). The dichroic (purple/green) Cr(VI) nitride, [HIPTN3N]CrN (8) was prepared from Bu4NN3 and 7. X-ray studies have been carried out on 4, 6, and 7, and on two co-crystallized compounds, 7 and [HIPTN3N]CrN3 (65:35) and [HIPTN3N]CrN3 and 8 (50:50). Exposure of a degassed solution of {1|2} to an atmosphere of ammonia does not yield "Cr(NH3)" as a stable and well-behaved species analogous to Mo(NH3). An attempt to reduce dinitrogen under conditions described for the catalytic reduction of dinitrogen by [HIPTN3N]Mo compounds with 8 yielded a substoichiometric amount (0.8 equiv) of ammonia, which suggests that some ammonia is formed from the nitride but none is formed from dinitrogen.

Nitrogen Fixation by a Molybdenum Catalyst Mimicking the Function of the Nitrogenase Enzyme: A Critical Evaluation of DFT and Solvent Effects

“…[11][12][13] However, an exhaustive understanding of this molecular processes is still lacking. 2,14 In an effort to further improve the efficiency of the catalyst, the transition-metal ion has been changed, 15,16 and the R group has been modified (R ) 3,5-(2,4,6-t-Bu 3 C 6 H 2 ) 2 C 6 H 3 , 3,5-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 , 4-Br-3,5-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 3 (p-Br(HIPT)). 17 Unfortunately, none of the modified complexes has turned out to show a stronger catalytic power than that of the original compound.…”

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] unter anderem weil Liganden [(RNCH 2 CH 2 ) 3 N] 3À mit 2,4,6-Triisopropylphenyl-, Mesityl-oder 2-Methylphenylgruppe als Rest R keinen Komplex mit Molybdän bilden. [31] Ziel beim Design des Liganden [HIPTN 3 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] [37] [HIPTN 3 N]W [38] und [HIPTN 3 N]V [39] die Reduktion von N 2 nicht katalysieren. Wir haben auch Mo-Komplexe untersucht, deren Liganden gegenüber [HIPTN 3 N] 3À leicht modifiziert waren, [40,41] und neuere Befunde bei der Reduktion von Distickstoff zusammengefasst.…”

“…36 h bei einem Druck von 15 psi (k = 5.3 10 À6 s À1 , DG°= 24.8 kcal mol À1 ), [34] 32 h bei 30 psi [42] und 30 h bei 55 psi. [42] Diese Werte legen nahe, dass der Austausch von 15 [37] Im analogen Molybdänkomplex mit Hexa(tert-butyl)-substituiertem Liganden, [HTBTN 3 N]Mo(N 2 ), verläuft der Austausch von 15 N 2 gegen N 2 etwa 20-mal langsamer (t 1/2 % 750 h bei 22 8C oder k = 2.6 10 À7 s À1 ) als in [HIPTN 3 N]Mo(N 2 ). Auch diese Reaktion ist druckunabhängig (k = 3.1 10 À7 s À1 bei 5 atm).…”

Molecular Catalysts for N2 Reduction: State of the Art, Mechanism, and Challenges

“…of ammonia per Mo atom. Most of the attempts to reproduce under different conditions or to improve the performances of the Schrock catalyst failed, by either modifying the type/amount of acid or the amide substituents of the ligand (only the HIPT and p ‐BrHIPT derivatives are catalytically active), or replacing molybdenum with other transition metals like vanadium, chromium or tungsten …”