Electrochemistry of carbidopentaruthenium C60 complexes and related clusters

The electrochemical behavior of the face-coordinated C-60-carbidopentaruthenium cluster complexes Ru5C(CO)(11)(PPh3)(mu(3)-eta(2),eta(2),eta(2)-C-60) (1), Ru5C(CO)(10)(mu-eta(1),eta(1)-dppf)(mu(3)-eta(2),eta(2),eta(2)-C-60) (2) (dppf = 1,1'-bis(diphenylphosphino)ferrocene), and PtRu5C(CO)(11)(eta(2)-dppe)(mu(3)-eta(2),eta(2),eta(2)-C-60) (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)(mu-eta(1),eta(1)-dppf) (6), PtRu5C(CO)(16) (7), and PtRu5C(CO)(14)(eta(2)-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 C-60 ligand. In contrast, similar scans for 2 indicate an initial quasi-reversible, one-electron reduction of the C-60 ligand that is dynamically coupled with a second one-electron, irreversible reduction. Stepwise reduction of the C-60 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 (nu(CO)) spectra.