Low-temperature deprotonation of the cationic mu-methylidyne complex [(Cp*Ru)(2)(mu-NPh)(mu-CH)][BF4] (Cp* = eta(5)-C5Me5) with KN(SiMe3)(2) affords a thermally unstable mu-carbido complex [(Cp*Ru)(2)(mu-NPh)(mu-C)] (2), as evidenced by trapping experiments with elemental S or Se and C-13 NMR spectroscopic observation. The reactivity of 2 toward CO2, Ph2S+CH2-, EtOH, and an intramolecular CH bond indicates that the mu-carbido carbon in 2 has an ambiphilic (nucleophilic and electrophilic) nature consistent with the formulation of 2 as the first example of a transition-metal-substituted singlet carbene. DFT study suggests that the Ru substituents in 2 are stronger sigma-donor and weaker pi-donor to the carbene center than amino substituents in N-heterocyclic carbenes.