We report the observation of the weakening of the RuC-Pt single bond in (Cy3P)(2)Cl2Ru equivalent to C-PtCl2-L (Ru equivalent to C-Pt-L) complexes, leading to the incipient formation of the terminal ruthenium carbide complex, (Cy3P)(2)Cl2Ru equivalent to C (RuC). In the solid state, elongation of RuC-Pt bonds illustrates the degree of weakening, and in solution, decreasing platinum-carbide coupling constants and increasing carbide chemical shifts reveal weaker interaction through the carbide bridge, as the electron donating ability of L becomes progressively stronger. For the bridging carbide ligands, the chemical shifts and coupling constants to platinum are linearly dependent, and NMR data for parent RuC conform to this relationship, providing a spectroscopic means of determining the strength of the RuC-Pt linkages relative to dissociated RuC. The pliancy of the Ru equivalent to C-Pt-L fragment with regard to the identity of L establishes the carbide-bridged complexes as remarkably wide-ranging and sensitive probes for ligand donor abilities.