The room-temperature reaction of [Os3(CO)12] with [PdCl(allyl)(NHC)], where NHC (N-heterocyclic carbene) = SIPr [N,N′-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene] or IPr [N,N′-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene], afforded Pd-Os mixed metal clusters with formulas of [PdnOs3(CO) 12(NHC)n] (n = 1-3). These are the first examples of Pd-Os heterometallic clusters containing NHC ligands, and they have all been structurally characterized. In all these clusters, the metal cores are raftlike, with carbonyl ligands bridging all the Os-Pd edges. © 2013 American Chemical Society.