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

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journal contribution
posted on 16.05.2005, 00:00 by Ming Li, Arkady Ellern, James H. Espenson
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 = {ka[L] + kb[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 kb/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 = ka[L]/{1 + κ[L]} × [{PhSReO(dt)}2]. For PPh3, values at 25.0 °C of ka/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.