Z-Selective Olefin Metathesis Reactions Promoted by Tungsten Oxo Alkylidene Complexes

Addition of LiOHMT (OHMT = O-2,6-dimesitylphenoxide) to W(O)(CH-t-Bu)(PMe2Ph)(2)Cl-2 led to WO(CH-t-Bu)Cl(OHMT)(PMe2Ph) (4). Subsequent addition of Li(2,5-Me2C4H2N) to 4 yielded yellow W(O)(CH-t-Bu)(OHMT)(Me(2)Pyr)(PMe2Ph) (5). Compound 5 is a highly effective catalyst for the Z-selective coupling of selected terminal olefins (at 0.2% loading) to give product in >75% yield with >99% Z configuration. Addition of 2 equiv of B(C6F5)(3) to 5 afforded a catalyst activated at the oxo ligand by B(C6F5)(3). 5.B(C6F5)(3) is a highly active catalyst that produces thermodynamic products (similar to 20% Z).