Diphosphine Mobility at a Binuclear Metal Center: A Concerted Double Trigonal-Twist in Bis(dithiolate) Complexes [M<sub>2</sub>(CO)<sub>4</sub>(μ-dppm){μ-S(CH<sub>2</sub>)<sub><i>n</i></sub>S}] (M = Fe, Ru; <i>n</i> = 2, 3)
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Heating [M2(CO)6{μ-S(CH2)nS}] (M = Fe, Ru; n = 2 (edt), 3 (pdt)) with bis(diphenylphosphino)methane (dppm) in toluene affords the bridged-diphosphine complexes [M2(CO)4(μ-dppm){μ-S(CH2)nS}]. At room temperature, all show two separate environments for the methylene protons of the diphosphine ligand, while at higher temperatures these coalesce to a single peak. This behavior, which interconverts the two sulfur atoms, is ascribed to a concerted double trigonal-twist of the M(CO)2P moieties. No such fluxional behavior was observed for the nonlinked dithiolate complexes [Fe2(CO)4(μ-dppm)(μ-SR)2] (R = Me, Ph, p-tolyl). The X-ray structures of [M2(CO)4(μ-dppm)(μ-edt)] (M = Fe, Ru) and [Fe2(CO)4(μ-dppm)(μ-SMe)2] are presented in order to compare them to the previously reported [M2(CO)4(μ-dppm)(μ-pdt)].
