Electrochemistry of carbidopentaruthenium C₆₀ complexes and related clusters

The electrochemical behavior of the face-coordinated C₆₀-carbidopentaruthenium cluster complexes Ru₅C(CO)₁₁(PPh₃(μ₃-η² ,η²,η²-C₆₀ (1) Ru₅C(CO)₁₀(μ-η¹,η¹-dppf)( μ₃-η²,η²,η²-C₆₀ ) (2) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), and PtRu₅C(CO)₁₁(η²-dppe)(μ₃- η²,η²,η²-C₆₀) (3) (dppe = 1,2-bis(diphenylphosphino)ethane) has been examined by cyclic voltammetry, rotating disk electrode voltammetry, and differential pulse voltammetry methods. The behavior of compounds Ru₅C(CO)₁₅ (4), Ru₅C(CO)₁₄(PPh₃) (5), Ru₅C(CO)₁₃(μ-η¹,η¹-dppf) (6), PtRu₅C(CO)₁₆ (7), and PtRu₅C(CO)₁₄(η²-dppe) (8) was studied also for comparison. For both 1 and 3, the voltammetric scans show an initial irreversible two-electron reduction feature, followed by three quasi-reversible, one-electron reductions of the C₆₀ ligand. In contrast, similar scans for 2 indicate an initial quasi-reversible, one-electron reduction of the C₆₀ ligand that is dynamically coupled with a second one-electron, irreversible reduction. Stepwise reduction of the C₆₀ ligand proceeds at more negative potentials. Interpretation of the electrochemical behavior of compounds 1-8 has been enhanced by studying their chemical reduction with cobaltocene. In all cases uptake of two electrons results in irreversible loss of a CO ligand from the cluster, and the resulting dianionic complexes have been characterized by their IR (ν_CO) spectra.