A transformative advance in chemistry has been the development of catalyst-controlled stereoselective olefin metathesis reactions; the original discovery, disclosed in 2009, and many of the subsequent related breakthroughs have been the result of research carried out in the laboratories of Professor Amir Hoveyda. During the past eight years the BC team has shown that incorporation of appropriate ligands within molybdenum-, tungsten (in collaboration with Professor Richard Schrock and co-workers at MIT) as well as ruthenium-based complexes has made formerly inaccessible reactivity and selectivity levels feasible. Now, graduate students Ming Joo Koh and Thach Nguyen and senior research fellow, Dr. Sebastian Torker, from the Hoveyda group together with postdoctoral fellows Dr. Jonathan Lam and Dr. Jakob Hyvl of the Schrock laboratories report in a Letter published in Nature (doi:10.1038/nature21043). that molybdenum monoaryloxide chloride (MAC) complexes furnish higher energy Z isomers of trifluoromethyl-substituted alkenes through cross-metathesis with commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. The latter reagent is an inexpensive, non-flammable widely used commercially as foam blowing agent and; additionally, it has zero ozone depleting potential and minimal global warming potential. Otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloro- and 1,2- dibromoethene can also be effected with substantially improved efficiency and Z selectivity. The importance of the new advance is highlighted through synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds. With the aid of DFT calculations, a logical basis for the origins of activity and selectivity levels, which contradict the previously proposed principles, has been provided.

See the recent publication by Richard Schrock and Amir Hoveyda:
Molybdenum chloride catalysts for Z-selective olefin metathesis reactions

(Ming Joo Koh, Thach T. Nguyen, Jonathan K. Lam, Sebastian Torker, Jakub Hyvl, Richard R. Schrock & Amir H. Hoveyda, Nature, doi:10.1038/nature21043)