SYNTHESIS AND SOLUTION STUDIES OF OS3(CO)9L(R2C2) (L=CO, MECN, P(OME)3 OR PPH3) - CRYSTAL AND MOLECULAR-STRUCTURE OF OS3(CO)9P(OME)3(PH2C2)

Reaction of Os3(CO)10(R2C2) (R = Ph, Et or Me) with 1.1 equivalent of Me3NO in the presence of MeCN at - 78°C produces a labilized cluster, Os3(CO)9(NCMe)-(R2C2), which upon reaction with alkyne (R′2C2) affords the known violet complex of formula Os3(CO)9(R2C2)(R′2C2), in which both the alkyne molecules are linked via a carbon-carbon bond to produce an osmacyclic ring. With simple phosphorus donor ligands L (where L = P(OMe)3, PPh3), the cluster Os3(CO)9(NCMe)(R2C2) affords the corresponding substituted complex Os3(CO)9L(R2C2) in yields of up to 80% yields. The structure of Os3(CO)9P(OMe)3(Ph2C2) has been established by a single crystal X-ray study. The structure is based on a triangular metal framework with the diphenylacetylene ligand bonded in a μ3-η2-|-bonding mode, forming two σ- and a π-bond with the osmium atoms, a P(OMe)3 ligand being attached to one osmium bearing a σ-bonded acetylenic carbon and occupying a pseudo equatorial position. 13C NMR studies have been carried out on the complex Os3(CO)9L(Me2C2) (L = CO, P(OMe)3 or PPh3) to give information about the structure in solution. The carbonyl ligands in all of these complexes are fluxional, and an intramolecular mechanism by which the carbonyls interchange between the three osmium atoms, in each complex, is discussed in detail. © 1990.