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