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 clust er 1,2-[Os-3(CO)(10)(mu -Ph2PCH2CH2SMe)], in which the phosphine and the th ioether 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 isomeriza tion 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 o f similar stability, with the latter isomer being of slightly lower energy. The dynamic behavior of the clusters have been investigated by variable-te mperature C-13{H-1} and P-31{H-1} NMR, and the kinetics of the isomerizatio n reaction have been measured. The latter indicate that the isomerization p roceeds via an associative mechanism which is proposed to involve an intram olecular nucleophilic attack by the coordinated sulfur on an osmium atom. T he 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.