A new hexanuclear cyclopentadienylnickel carbide cluster (NiCp)(6)(mu(6)-C) (1) was obtained through the thermolysis of the alkene complex [NiCp(CH3)(eta(2)-CH2=CHC4H9)] (4). The X-ray molecular structure of 1 (monoclinic; P2(1)/c; Ni-C-carbide = 1.767(4)-2.109(4) angstrom) reveals a highly deformed octahedral arrangement of nickel atoms with two octahedron edges opened (Ni-Ni bonding distances = 2.410(1)-2.623(1) angstrom, Ni center dot center dot center dot Ni nonbonding distances = 3.107(2) and 3.108(2) angstrom). Cluster 1 is the first example of a homoleptic, cyclopentadienylnickel carbide cluster. Moreover, C-13-labeling studies proved that the carbido ligand in cluster 1 originated from the Ni-bound methyl group. This transformation requires a triple C-H bond activation in the methyl group, which has not been observed so far for late transition metal compounds.