Activation of the S−S Bonds of Alkyl Disulfides RSSR (R = Me, Et, Pr, Buⁿ) by Heterodinuclear Phosphido-Bridged CpW(CO)₂(μ-PPh₂)Mo(CO)₅

Reactions of (1) with alkyl disulfides RSSR (R = Me, Et, Pr, Buⁿ) in refluxing dichloromethane yielded the series of new mixed-metal and mixed-ligand bridged compounds (R = Me (4a), Et (4b), Pr (4c), Buⁿ (4d)), (R = Me (5a), Et (5b), Pr (5c), Buⁿ (5d)), and (R = Me (6a), Et (6b), Pr (6c), Buⁿ (6d)). All except 6c were characterized by single-crystal X-ray diffraction analysis. Formation of compounds 4−6 indicates a general procedure for cleavage of the S−S bonds of alkyl disulfides under mild conditions. Molecular structures of compounds 6a,b,d reveal the first transformation of the bridging PPh₂ ligand of 1 to give the hybrid ligands Ph₂PSR (R = Me, Et, Buⁿ) via P−S bond formation. The average Mo−W bond distance (2.8255 Å) in the 34e dimers (4a−d, 6a,b,d) is shorter than that in the 32e dimers (5a−d), 2.8494 Å. This appears quite unusual, according to the 18e rule. DFT calculations have been performed to investigate this unusual observation. Characterization of the substitution products (7) and (8; COD = cyclooctadiene) leads to the conclusion that carbonyl ligands on the Mo sites are more labile than those on the W sites.