Synthesis, Characterization, and Novel Fluxional Mechanisms of Triosmium Clusters Containing the Highly Flexible Ligand Ph2PC2H4SC2H4SC2H4PPh2 (PSSP)

Treatment of Ph2PC2H4SC2H4SC2H4PPh2 (PSSP) with [Os-3(CO)(11)(NCMe)] under mild conditions yields [{Os-3(CO)(11)}(2)(mu-PSSP)], 1, and [Os-3(CO)(11)(PSSP)], 2. In cluster 1 the ligand links two trinuelear cluster subunits, coordinating via its phosphine moieties. In cluster 2, the ligand is coordinated through one of the phosphine groups, while the remaining part of the PSSP ligand is oriented in a dangling mode. Treatment of [Os-3(CO)(11)(NCMe)(2)] with PSSP yields 1,2-[Os-3(CO)(10)(PSSP)], 3. NMR data presented in this paper indicate that a concerted cis/trans isomerism with respect to the phosphines operates in the cluster. This type of process has not been observed previously for a bridging ligand, but has been detected in the case of corresponding triosmium clusters with bis-monodentate phosphine ligands. Oxidative decarbonylation of [{Os-3(CO)(11)}(2)(mu-PSSP)], 1, with Me3NO yields cluster [{Os-3(CO)(10)}(2)(mu-PSSP)], 4. This cluster consists of two P,S-bridged cluster units. In solution at room temperature, 4 undergoes a slow rearrangement from a 1,2-bridging to a 1,1-chelating coordination mode. The crystal structures of clusters 1, 3, and 4 are reported.