Latent ruthenium olefin metathesis catalysts that contain an N-heterocyclic carbene ligand

A new N-heterocyclic carbene containing olefin metathesis catalyst, (sIMes)(Cl)(2)Ru(CH(CH2)(2)-C,N-2-C5H4N) (4a), was synthesized from (sIMes)(PCy3)(Cl)(2)-Ru=CHPh (1) or (sIMes)(Py)(2)(Cl)(2)Ru=CHPh (3). When heated at 40 degreesC in dichloromethane, 4a is slowly converted to its isomer 4b. The X-ray structures of 4a and 4b show that the NHC and pyridine ligands are trans in 4a and cis in 4b. 4a is more latent than 1 and 4b much more latent than 4a in ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP).