Catalytic Silylation of Dinitrogen with a Dicobalt Complex

Abstract

A dicobalt complex catalyzes N2 silylation with Me3SiCl and KC8 under 1 atm N2 at ambient temperature. Tris(trimethylsilyl)amine is formed with an initial turnover rate of 1 N(TMS)3/min, ultimately reaching a turnover number of ∼200. The dicobalt species features a metal-metal interaction, which we postulate is important to its function. Although N2 functionalization occurs at a single cobalt site, the second cobalt center modifies the electronics at the active site. Density functional calculations reveal that the Co-Co interaction evolves during the catalytic cycle: weakening upon N2 binding, breaking with silylation of the metal-bound N2 and reforming with expulsion of [N2(SiMe3)3](-).

Silylation of Dinitrogen Catalyzed by Hydridodinitrogentris(Triphenylphosphine)Cobalt(I)

“…One could expect that [CoN2(PPh3)3] − should directly react with Me3SiCl, resulting in the formation of Si-N bonds, similarly to the dinuclear system reported by the groups of Gagliardi and Lu [33]. However, as shown by Nishibayashi, Yoshizawa and co-workers, many simple cobalt complexes reveal long incubation periods before the onset of the catalytic reaction [34].…”

“…It is possible that this species is being transformed into the actual catalyst during the incubation period. Since good molecular catalysts for the silylation of dinitrogen can reach over 200 turnovers [25,33], it is plausible that the actual very active catalyst is present only in minute amounts, which prevents its spectroscopic characterization. Based on the work of Nishibayashi, Yoshizawa and co-workers, an in-situ formed metallosilane species [28,34] can be responsible for the catalytic activity of CoH(PPh 3 ) 3 N 2 .…”

“…Peters and co-workers reported methylation and trimethylsilylation of dinitrogen bound to [(PhB(CH2P i Pr2)3)CoN2]2Mg(THF)4 ( Figure 3) [32]. Last year, Gagliardi, Lu and co-workers reported a dinuclear cobalt complex that catalyzes the formation of N(SiMe3)3 from dinitrogen with an impressive turnover number of 195 [33], while the group of Nishibayashi showed that in the presence of 2-2'-bipyridine, Co2(CO)8 can catalyze the formation of up to 49 equivalents of N(SiMe3)3 ( Figure 2) [34]. Homogeneous cobalt complexes with tris(phosphine)borate ligands were also shown by Peters and co-workers to catalyze the formation of over two equivalents of ammonia [35].…”

3-Methylindole-Based Tripodal Tetraphosphine Ruthenium Complexes in N2 Coordination and Reduction and Formic Acid Dehydrogenation

“…Therefore, we set out to explore the reactivity of the tripodal tetraphosphine ruthenium(II) complexes for dinitrogen reduction with chlorosilanes ( Figure 11), which follows a different mechanism [24]. A mixture of the RuCl 2 L complexes with 100 equiv of KC 8 and 100 equiv of chlorotrimethylsilane in 10 mL THF at room temperature under an atmosphere of dinitrogen was stirred for 1 day, whereafter an aliquot of the reaction mixture was analyzed by GC. Modest yields of~1.5 equivalents of (Me 3 Si) 3 N relative to Ru were detected, regardless of the complex used (Table 3).…”

“…Electronic effects in the ligands translated to a change in the N≡N stretch frequency of the coordinated dinitrogen. The complexes were studied in the N 2 reduction with chlorosilanes and KC 8 , yielding stoichiometric amounts of the silylamines. When the reaction was followed in time, an incubation period was observed.…”