Olefin Metathesis Reactions with Vinyl Halides: Formation, Observation, Interception, and Fate of the Ruthenium−Monohalomethylidene Moiety

Ru(CHPh)(H2IMes)(PCy3)Cl2 (2) reacts with vinyl chloride to form Ru(CHCl)(H2IMes)(PCy3)Cl2 (8) and styrene. Complex 8 is thermally unstable and decomposes rapidly to phosphoniocarbene complex Ru(CHPCy3)(H2IMes)Cl3 and/or carbide complex Ru(⋮C:)(H2IMes)(PCy3)Cl2, depending on conditions. However, 8 can be observed at low temperature and can be trapped by alkyne, as shown by enyne metathesis of vinyl chloride with trimethylsilylacetylene. Vinyl bromide reacts similarly with 2.