Synthesis, Structure, and Reactivity of Organoruthenium Derivatives of Tetrathio-and Tetraselenometalates

We describe the preparation of a series of organoruthenium tetrathiometalates and tetraselenometalates of the general formula (RC₅H₄)₂Ru₂L₂ME ₄ (R = H, CH₃; L = PR₃, RNC, CO; M = W, Mo; E = S, Se). The compound Cp₂Ru₂(PPh₃)₂WS₄ (1) reacts with PMe₃ to give Cp₂Ru₂(PMe₃)₂WS₄ and with isocyanides to give Cp₂Ru₂(RNC)₂WS₄ (R = t-Bu, Me, C₆H₅CH₂). Only one of the PPh₃ ligands in 1 is substituted by an excess of carbon monoxide to give Cp₂Ru₂(PPh₃)(CO)WS₄. The kinetics of the ligand substitution of 1 by t-BuNC was examined by using ¹H NMR spectroscopy. The rate of the first substitution was found to be independent of [t-BuNC], the first-order rate constant being 5.6 × 10^-4 s^-1. The rate of the first substitution was found to be approximately 4 times that of the second. All of the compounds studied undergo reversible or quasi-reversible oxidations. On the basis of the measured E_1/2 values, the donor powers of the chalcogenometalates are ranked as follows: MoSe₄^2- > WSe₄^2- > MoS₄^2- > WS₄^2-. The compound Cp₂Ru₂(MeNC)₂WS₄ crystallizes in the monoclinic space group I2/a with a = 13.840 (13) Å, b = 12.234 (9) Å, c = 14.224 (11) Å, β = 105.48 (7)°, V = 2321 (3) ų, and Z = 4 and refined to R = 0.038 and R_w = 0.049. The short Ru-W distances (2.870 (2) Å) and the acute Ru-S-W angles (77° average) are indicative of metal-metal bonding. The reactivity, redox properties, and structures of these compounds are discussed in the context of the donation of t_2g electrons on ruthenium to tungsten.