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.将化合物(1)与烷基二硫化物RSSR（R为Me、Et、Pr、Bun）在回流二氯甲烷中反应，得到一系列新型混合金属-混合配体桥联化合物，分别为对应R=Me的4a、R=Et的4b、R=Pr的4c、R=Bun的4d（4系列），对应R=Me的5a、R=Et的5b、R=Pr的5c、R=Bun的5d（5系列），以及对应R=Me的6a、R=Et的6b、R=Pr的6c、R=Bun的6d（6系列）。除化合物6c外，其余所有产物均通过单晶X射线衍射分析完成表征。化合物4至6的成功合成，为温和条件下烷基二硫化物的S-S键断裂提供了通用合成策略。化合物6a、6b、6d的分子结构揭示了首例通过P-S键形成，将化合物1的桥联二苯基膦（PPh₂）配体转化为杂化配体Ph₂PSR（R为Me、Et、Bun）的过程。34电子二聚体（4a~4d、6a、6b、6d）的平均Mo-W键长（2.8255 Å）短于32电子二聚体（5a~5d）的平均键长（2.8494 Å）。根据18电子规则，这一现象颇为反常。我们通过密度泛函理论（DFT）计算对这一反常现象展开了研究。对取代产物7与8（其中COD为环辛二烯（cyclooctadiene））的表征结果表明，钼（Mo）位点的羰基配体比钨（W）位点的羰基配体更易发生解离。