Treatment of [Fe2(mu-pdt)(CO)6] [pdt=S(CH2)3S] with dppe (Ph2PCH2CH2PPh2) in refluxing toluene affords the asymmetric complex [Fe2(mu-pdt)(CO)4(dppe)] (1). Protonation of 1 with HBF4-Et2O in CH2Cl2 gives at room temperature the mu-hydrido derivative [Fe2(mu-pdt)(CO)4(dppe)(mu-H)](BF4) (2). Monitoring the reaction by 1H, 31P, and 13C NMR at low temperature reveals unambiguously that the process of the protonation of 1 implies terminal hydride intermediates.

International audienceTreatment of [Fe2(µ-pdt)(CO)6] (pdt = S(CH2)3S) with 1,10-phenanthroline (phen) in refluxing toluene affords the asymmetric complex [Fe2(µ-pdt)(CO)4(phen)] (1); the protonation of 1 with HBF4·OEt2 in CD2Cl2 at 203 K has been monitored by 1H NMR

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A novel unsymmetrically disubstituted propanedithiolate compound [Fe 2 (CO) 4 (k 2 -dmpe)(m-pdt)] (1) (pdt ¼ SCH 2 CH 2 CH 2 S, dmpe ¼ Me 2 PCH 2 CH 2 PMe 2 ) was synthesized by treatment of [Fe 2 (CO) 6 (m-pdt)] with dmpe in refluxing THF. Compound 1 was characterized by single-crystal X-ray diffraction analysis. Protonation of 1 with HBF 4 $Et 2 O in CH 2 Cl 2 gave at room temperature the m-hydrido derivative [Fe 2 (CO) 4 (k 2 -dmpe)(m-pdt)(m-H)](BF 4 )] (2). At low temperature, 1 H and 31 Pe{ 1 H} NMR monitoring revealed the formation of a terminal hydride intermediate 3. Comparison of these results with those of a VT NMR study of the protonation of symmetrical compounds [Fe 2 (CO) 4 L 2 (m-pdt)] [L ¼ PMe 3 , P(OMe) 3 ] suggests that in disubstituted bimetallic complexes [Fe 2 (CO) 4 L 2 (m-pdt)], dissymmetry of the complex is required to observe terminal hydride species. Attempts to extend the series of chelate compounds [Fe 2 (CO) 4 (k 2 -L 2 )(m-pdt)] by using arphos (arphos ¼ Ph 2 AsCH 2 CH 2 PPh 2 ) were unsuccessful. Only mono-and disubstituted derivatives [Fe 2 (CO) 6Àn (Ph 2 AsCH 2 CH 2 PPh 2 ) n (m-pdt)] (n ¼ 1, 4a; n ¼ 2, 4b), featuring dangling arphos, were isolated under the same reaction conditions of formation of 1. Compound 4b was structurally characterized.

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