Molybdenum- and tungsten-based olefin metathesis catalysts have demonstrated excellent results in the control of cis (Z-) selectivity as well as enantioselectivity. However, their air and moisture sensitivity, which requires the use of a glovebox, has prevented their more widespread use by organic chemists. Now we report on developed, preweighed Mo catalysts formulated in paraffin tablets.
The significantly improved air stability, high homogeneity, and uniformity of the pellets allow researchers to carry out reactions on the bench avoiding the need of a glovebox.
The two different Mo-based complexes which were packed into tablets are XiMoPac-Mo001 (1) that can be used to achieve endo-selective enyne ring-closing metathesis (RCM) reactions, interalia; and XiMoPac-Mo003 (2) which was reported among the best catalysts to promote Z-selective cross-metathesis.
For the evaluation of the wax-protected catalysts commonly used, highly reproducible robust model reactions were chosen: homo cross-metathesis (HCM) of functionalized (e.g., methyl 9-decenoate) and unfunctionalized (allylbenzene) terminal olefins, and ring closing metathesis (RCM) of diethyl diallylmalonate. The yields and conversions were comparable with those which can be achieved in glovebox with nonformulated catalysts.
Exposure to air did not cause any significant reduction in conversion while the product selectivity (targeted product vs homologues derived from double bond isomerization) remained high. In contrast, exposure to air caused a measurable drop in the conversion with the nonprotected catalyst. Furthermore, the formulated catalysts remained unaffected even after 4 h of exposure to air, showing its enhanced air stability.
In conclusion, these commercially available air-stable Mo-catalyst tablets allow the reactions to be accomplished using ordinary Schlenk techniques, and hence simplify catalyst handling in pilot laboratories and plants.
From Box to Bench: Air-Stable Molybdenum Catalyst Tablets for Everyday Use in Olefin Metathesis
- Over 30 years experience in the Swiss chemical industry
- Over 20 years in the fragrance and flavor industry, five as Research Director for Givaudan
- Former President Swiss Chemical Society (SCS)
- Former Professor at the University of Zürich
- Current member of the board of Thales Nano