Basal site substitution in the sulfide-bridged cluster Ru-3(CO)(9)(mu(3)-S)(2) by the redox-active diphosphine 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). Synthesis, X-ray structure and electrochemical properties of Ru-3(CO)(7)(bpcd)(mu-S)(2)

The sulfide-bridged cluster Ru-3(CO)(9)(mu(3)-S)(2) (1) has been allowed to react with the redox-active diphosphine ligand 4,5-bis(diphenylphosphino) -4-cyclopenten-1,3-dione (bpcd) in the presence of Me(3)NO to give the new cluster Ru-3(CO)(7)(bpcd)(mu(3)-S)(2) (2) in 61% yield. The ancillary bpcd in 2 is bound at one of the basal ruthenium sites in a chelating fashion, being derived by the replacement of axial and equatorial CO groups. This cluster represents the first example of a cluster derived from Ru-3(CO)(9)(mu(3)-S)(2) that contains a chelating diphosphine ligand. Cluster 2 has been characterized in solution by IR and NMR (H-1 and P-31) spectroscopies and in the solid state by X-ray diffraction analysis. Ru-3(CO)(7)(bpcd)(mu(3)-S)(2), which exists as two crystallographically independent molecules in the unit cell, crystallizes in the monoclinic space group P2(1)/c, a = 19.451(1), b = 21.865(2), c = 20.982(2) Angstrom, beta = 116.011(6)degrees, V = 8019.7(10) Angstrom(3), Z=8, D-calc = 1.702 g cm(-3); R = 0.0411, R(w) = 0.0447 for 5622 observed reflections. The redox properties of 2 were explored by cyclic voltammetry in MeCN, which revealed the presence of a reversible one-electron reduction process (bpcd based) and an irreversible oxidation (metal based). The nature of the HOMO and LUMO in 2 has been examined by carrying out extended Huckel MO calculations on the model cluster Ru-3(CO)(7)(H-4-bpcd)(mu(3)-S)(2), and the results are discussed relative to the observed electrochemistry.