A novel unsymmetrically disubstituted propanedithiolate compound [Fe 2 (CO) 4 (κ 2 -dmpe)(μ-pdt)] ( 1 ) (pdt = SCH 2 CH 2 CH 2 S, dmpe = Me 2 PCH 2 CH 2 PMe 2 ) was synthesized by treatment of [Fe 2 (CO) 6 (μ-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 μ-hydrido derivative [Fe 2 (CO) 4 (κ 2 -dmpe)(μ-pdt)(μ-H)](BF 4 )] ( 2 ). At low temperature, 1 H and 31 P–{ 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 (μ-pdt)] [L = PMe 3 , P(OMe) 3 ] suggests that in disubstituted bimetallic complexes [Fe 2 (CO) 4 L 2 (μ-pdt)], dissymmetry of the complex is required to observe terminal hydride species. Attempts to extend the series of chelate compounds [Fe 2 (CO) 4 (κ 2 -L 2 )(μ-pdt)] by using arphos (arphos = Ph 2 AsCH 2 CH 2 PPh 2 ) were unsuccessful. Only mono- and disubstituted derivatives [Fe 2 (CO) 6− n (Ph 2 AsCH 2 CH 2 PPh 2 ) n (μ-pdt)] ( n = 1, 4a ; n = 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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Ezzaher et al. (2008) studied this question.