Synthesis of characterization of triosmium clusters containing the bidentate ligand Ph2PCH2CH2SMe: Detection of an isomerization reaction involving bridging and chelating ligand coordination modes

Article abstract of DOI:10.1021/om010223d

Diphenylphosphinoethylene methyl sulfide, Ph₂PCH₂CH₂SMe, reacts with [Os₃(CO)₁₁-(NCMe)] yielding [Os₃(CO)₁₁(Ph₂PCH₂ CH₂SMe)]. Treatment of [Os₃(CO)₁₀ (NCMe)₂] with 1 equiv of the P,S ligand initially yields the cluster 1,2-[Os₃(CO)₁₀(μ-Ph₂PCH₂ CH₂SMe)], i which the phosphine and the thioether moieties coordinate to different metal atoms of the metal triangle; addition of two or more equivalents of the ligand yields 1,2-[Os₃(CO)₁₀ (μ-Ph₂PCH₂CH₂SMe)] and [Os₃(CO)₁₀(Ph₂PCH₂CH₂SMe) ₂]. The cluster 1,2-[Os₃(CO)₁₀(μ-Ph₂PCH₂ CH₂SMe)] is metastable and undergoes a slow isomerization reaction at room temperature to form 1,1-[Os₃(CO)₁₀(Ph₂PCH₂CH₂ SMe)], in which the ligand chelates one Os atom. Computational modeling of 1,2- and 1,1-[Os₃(CO)₁₀(Ph₂PCH₂ CH₂ SMe)] indicates that the two clusters are of similar stability, with the latter isomer being of slightly lower energy. The dynamic behavior of the clusters have been investigated by variable-temperature ¹³ C{¹H} and ³¹P{¹H} NMR, and the kinetics of the isomerization reaction have been measured. The latter indicate that the isomerization proceeds via an associative mechanism which is proposed to involve an intramolecular nucleophilic attack by the coordinated sulfur on an osmium atom. The solid state structures of [Os₃(CO)₁₁ (Ph₂PCH₂CH₂SMe)]. 1,2-[Os₃(CO)₁₀(μ-Ph₂PCH₂ CH₂SMe)], and 1,1-[Os₃(CO)₁₀(Ph₂PCH₂CH₂ SMe)] are reported.