N-Heterocyclic Carbene−Osmium Complexes for Olefin Metathesis Reactions

The complexes [(η6-p-cymene)OsCl(CHPh)(IPr)]OTf (4a; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene) and [(η6-p-cymene)OsCl(CHPh)(IMes)]OTf (4b; IMes = 1,3-bis(2,4,6-trimethylphenyl)imida-zolylidene) have been prepared by reaction of the corresponding 16-electron compounds [(η6-p-cymene)OsCl(NHC)]OTf (NHC = IPr (3a), IMes (3b)) with phenyldiazomethane, and their potential as initiators for olefin CM, RCM, and ROMP reactions has been explored.