Cationic Tungsten(VI) Penta-Methyl Complex: Synthesis, Characterization and its Application in Olefin Metathesis Reaction

Abstract

-Tungsten-hexa-methyl readily reacts with B(C 6 F 5 ) 3 in dichloromethane and generates the corresponding well-defined cationic tungsten-penta-methyl complex which was identified precisely by 1 H NMR, 13 C NMR, 1 H-13 C NMR correlation spectroscopy. Unlike WMe 6 , this cationic complex has low energy barrier to form tungsten carbene intermediate, which was further supported by the fact that WMe 6 alone has no activity in olefin metathesis reaction whereas the cationic complex shows catalytic activity for self-metathesis of 1-octene. C RMN, 1 H-13 C RMN. À la différence du WMe 6 , ce complexe cationique a une barrière énergétique faible pour former un intermédiaire de carbène tungstène, ce qui a été ultérieurement étayé par le fait que le WMe 6 seul n'a pas d'activité dans la réaction de métathèse des oléfines, tandis que le complexe cationique montre une activité catalytique pour l'autométathèse d'1-octène.

Synthesis and characterization of a homogeneous and silica supported homoleptic cationic tungsten(vi) methyl complex: application in olefin metathesis

“…14b We also found in the 1 H- 13 C correlation spectra that the peak at 0.5 ppm in the 1 H-NMR spectrum correlates with the peak at 10.8 ppm in the 13 C-NMR spectrum and the peak at 2.7 ppm in the 1 H-NMR spectrum correlates with the peak at 103.2 ppm in the 13 C-NMR spectrum. In separate experiments we synthesised 13 C labelled W(C 13 H 3 ) 6 and upon treatment with B(C 6 F 5 ) 3 in dichloromethane solution we have identified the incorporation of the labelled methyl into the [(C 13 H 3 )B(C 6 F 5 ) 3 ] À anion, in the final product. The above experiment clearly indicated that the methyl that bears [MeB(C 6 F 5 ) 3 ] À came from WMe 6 .…”

“…1d) almost completely disappeared in less than 15 minutes with the formation of two new peaks at 2.7 and 0.48 ppm in the 1 H-NMR spectrum (Fig. 1a) and 103.2 and 10.8 ppm in the 13 C NMR spectrum (Fig. 1a and b).…”

“…Similarly the 13 C-NMR spectra also clearly show that the peak at 82.2 ppm of WMe 6 also completely disappeared with the formation of two new peaks at 103.2 ppm for [W(CH 3 ) 5 ] + and 10.8 ppm corresponding to [(CH 3 )B(C 6 F 5 ) 3 ] À which is in good agreement with the literature value reported for the anion [(CH 3 )B(C 6 F 5 ) 3 ] À . 14b We also found in the 1 H- 13 C correlation spectra that the peak at 0.5 ppm in the 1 H-NMR spectrum correlates with the peak at 10.8 ppm in the 13 C-NMR spectrum and the peak at 2.7 ppm in the 1 H-NMR spectrum correlates with the peak at 103.2 ppm in the 13 C-NMR spectrum. In separate experiments we synthesised 13 C labelled W(C 13 H 3 ) 6 and upon treatment with B(C 6 F 5 ) 3 in dichloromethane solution we have identified the incorporation of the labelled methyl into the [(C 13 H 3 )B(C 6 F 5 ) 3 ] À anion, in the final product.…”

“…2 Subsequently, we switched to an organic Lewis acid, tris(pentafluorophenyl)boron which is known to form a non-nucleophilic anion after de-methylation reaction. 13 The reaction was monitored by NMR at À20 1C, and it was found that the reaction between WMe 6 and B(C 6 F 5 ) 3 was very fast and the peaks corresponding to WMe 6 at 1.75 ppm in the 1 H-NMR spectrum (Fig. 1c) and 82.2 ppm in the 13 C NMR spectrum (Fig.…”

“…13 The reaction was monitored by NMR at À20 1C, and it was found that the reaction between WMe 6 and B(C 6 F 5 ) 3 was very fast and the peaks corresponding to WMe 6 at 1.75 ppm in the 1 H-NMR spectrum (Fig. 1c) and 82.2 ppm in the 13 C NMR spectrum (Fig. 1d) almost completely disappeared in less than 15 minutes with the formation of two new peaks at 2.7 and 0.48 ppm in the 1 H-NMR spectrum (Fig.…”