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

Diphenylphosphinoethylene methyl sulfide, Ph2PCH2CH2SMe, reacts with [Os-3(CO)(11)-(NCMe)] yielding [Os-3(CO)(11)(Ph2PCH2CH2SMe)]. Treatment of [Os-3(CO)(10)(NCMe)(2)] with 1 equiv of the P,S ligand initially yields the cluster 1,2-[Os-3(CO)(10)(mu -Ph2PCH2CH2SMe)], in 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-[Os-3(CO)(10)(PPh2PCH2CH2SMe)] and [Os-3(CO)(10)(Ph2PCH2CH2SMe)(2)]. The cluster 1,2-[Os-3(CO)(10)(mu -Ph2PCH2CH2SMe)] is metastable and undergoes a slow isomerization reaction at room temperature to form 1,1-[Os-3(CO)(10)(Ph2PCH2CH2SMe)], in which the ligand chelates one Os atom. Computational modeling of 1,2- and 1,1-[Os-3(CO)(10)(Ph2PCH2CH2SMe)] 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 C-13{H-1} and P-31{H-1} 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 [Os-3(CO)(11)(Ph2PCH2CH2SMe)] 1,2-[Os-3(CO)(10)(mu -Ph2PCH2CH2SMe)], and 1'1-[Os-3(CO)(10)(Ph2PCH2CH2SMe)] are reported.