Weakening of Carbide-Platinum Bonds as a Probe for Ligand Donor Strengths.

We report the observation of the weakening of the RuC-Pt single bond in (CyP)ClRu≡C-PtCl-L (Ru≡C-Pt-L) complexes, leading to the incipient formation of the terminal ruthenium carbide complex, (CyP)ClRu≡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≡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.