Latent ruthenium olefin metathesis catalysts featuring a phosphine or an N-heterocyclic carbene ligand

The synthesis and characterization of latent 18-electron ruthenium benzylidene complexes (PCy₃)((^κN,O)-picolinate)₂RuCHPh (5) and (H₂IMes)((^κN,O)-picolinate)₂RuCHPh (6) are described. Both complexes appear as two isomers. The ratio between the isomers is dependent on l-type ligand. The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli. Upon addition of HCl, complexes 5 and 6 become highly active in olefin metathesis reactions. The advantage of the latent catalysts is demonstrated in the ring-opening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation. Trapping experiments suggests that the acid converts the 18-electron complexes into their corresponding highly olefin metathesis active 14-electron benzylidenes.