The recent discovery of stable 14 electron ruthenium phosphonium
alkylidenes related to the Grubbs olefin metathesis catalyst portfolio has
allowed us to probe the properties of the intermediates in the catalytic
cycle for this important reaction. The synthesis and properties of these
phosphonium alkylidenes will be discussed, and their conversion into
ruthenacyclobutanes via reaction with olefins will be presented. Detailed
NMR spectroscopic studies reveal the structural and dynamic properties of
these previously unobservable intermediates.