Rhenium(V) Complexes with Thiolato and Dithiolato Ligands:  Synthesis, Structures, and Monomerization Reactions

The new compound {(PhS)₂ReO(μ-SPh)}₂, 1, was synthesized from Re₂O₇ and PhSH and then used as the synthon for a number of hitherto unknown oxorhenium(V) compounds. Reactions between dithiols and 1 (2:1 ratio) afford {PhSReO(dt)}₂, where the dithiols, dtH₂, are 1,2-ethanedithiol (edtH₂), 1,3-propanedithiol (pdtH₂), 1,3-butanedithiol (pdtMeH₂), 1,2-benzenedithiol (bdtH₂), 2-(mercaptomethyl)thiophenol (mtpH₂), and 2-mercaptoethyl sulfide (mesH₂). Similar reactions carried out with a 3:1 ratio of dtH₂ to 1 afford [(ReO)₂(dt)₃], dt = edt, pdt. When NEt₃ was introduced prior to the 3:1 reaction between edtH₂ and 1, a compound containing an anionic complex was isolated, [PPh₄][ReO(edt)₂]. The new compounds were characterized analytically, spectroscopically, and crystallographically. The Re−O groups in two of the compounds, 1 and {ReO(μ-SPh)(bdt)}₂, exist in rare anti orientations; the others adopt the more familiar syn geometry, as discussed. Selected monomerization reactions of {PhSReO(dt)}₂ were also carried out:  {PhSReO(dt)}₂ + 2L = 2[PhSReO(dt)L]. The rate for L = 4-phenylpyridine is given by v = {k_a[L] + k_b[L]²} × [{PhSReO(dt)}₂], as it is for the reactions of {MeReO(dt)}₂; for all of these compounds, the reaction proceeds nearly entirely by the third-order pathway. Values of k_b/L² mol^-2 s^-1 at 25.0 °C are 5.8 × 10² (mtp), 2.97 × 10³ (pdt), 4.62 × 10⁵ (edt), and 3.87 × 10⁵ (bdt). The rate law for the reactions of {PhSReO(dt)}₂ with L = PAr₃ is v = k_a[L]/{1 + κ[L]} × [{PhSReO(dt)}₂]. For PPh₃, values at 25.0 °C of k_a/L mol^-1 s^-1 (κ/L mol^-1) for {PhSReO(dt)}₂ are 9.64 × 10^-2 (1.87) for mtp, 3.43 × 10^-2 (0.492) for pdt, 1.91 (1.42) for edt, 1.84 × 10^-2 (0.82) for bdt, and 1.14 × 10³ (10.6) for 1. Mechanisms are proposed that are consistent with the data obtained and with earlier work.