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

Wojciech Dzik

doi:10.3390/inorganics4030021

Abstract

Recently, homogeneous cobalt systems were reported to catalyze the reductive silylation of dinitrogen. In this study the investigations on the silylation of dinitrogen catalyzed by CoH(PPh3)3N2 are presented. We show that in the presence of the title compound, the reaction of N2 with trimethylsilylchloride and sodium yields, on average, 6.7 equivalents of tris(trimethylsilyl)amine per Co atom in THF (tetrahydrofuran). The aim was to elucidate whether the active catalyst is: (a) the [Co(PPh3)3N2]− anion formed after two-electron reduction of the title compound; or (b) a species formed via decomposition of CoH(PPh3)3N2 in the presence of the highly reactive substrates. Time profile, and IR and EPR spectroscopic investigations show instability of the pre-catalyst under the applied conditions which suggests that the catalytically active species is formed through in situ modification of the pre-catalyst.

Highlights

Effective catalytic activation of dinitrogen under ambient conditions remains one of the biggest challenges in synthetic chemistry
The cobalt-dinitrogen complex CoH(PPh3)3N2 is a pre-catalyst in the reductive silylation of the dinitrogen reaction
This complex itself does not mediate the formation of N–Si bonds; under the applied catalytic conditions it transforms to the active species after approximately 4 h

Summary

IInnttrroodduuccttiioonn

Effective catalytic activation of dinitrogen under ambient conditions remains one of the biggest challenges in synthetic chemistry. Potassium gave good results with other systems [26] and the failure to obtain the desired product with this reductant is likely caused by a very fast reaction of potassium (disappearance of all solids within less than an hour) with all Me3SiCl before the catalytically active species could be formed (see below). Measurements of the clear, brown solution obtained after sedimentation of the insoluble material formed during the catalytic reaction revealed a bimodal distribution of particles with an average size of 20 and 100 nm (see Figures S2 and S3 in the supplementary materials) This solution was, no longer active in the silylation of N2 when additional sodium and Me3SiCl were added. This suggests that even if cobalt nanoparticles are formed, they are an unlikely catalyst for the title reaction. 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(PPh3)3N2

Materials and Methods

Findings

Conclusions