Heteronuclear transition metal-alkyne clusters. Part 2. Formation of trinuclear clusters via reactions of [W(CO)(R1C2R2)(S2CNR2)2](R1= R2= Ph or H, R = Me or Et; R1= R2= R = Me; R1= Ph, R2= H, R = Et) with octacarbonyldicobalt. X-Ray crystal structure of [WCo2(µ-S)(µ-SCNEt2)(CO)4(C2Ph2)(S2CNEt2)]

Abstract

Reactions between [W(CO)(R¹C₂R²)(S₂CNR₂)₂](R¹= R²= Ph or H, R = Me or Et; R¹= R²= R = Me; R¹= Ph, R²= H, R = Et) and [Co₂(CO)₈] afford the trinuclear metal complexes [WCo₂(µ-R¹C₂R²)(µ-S)(CO)₅(SCNR₂)(S₂CNR₂)] which have been characterised by analytical and spectroscopic methods. All the compounds, except the ethyne derivatives, undergo carbonyl loss and rearrangement in solution to afford [WCo₂(µ-S)(µ-SCNR₂)(CO)₄(R¹C₂R²)(S₂CNR₂)]. The molecular structure of [WCo₂(µ-S)(µ-SCNEt₂)(CO)₄(C₂Ph₂)(S₂CNEt₂)] has been established by an X-ray diffraction study. The cluster has a triangular metal framework [W-Co 2.701 (1) and 2.601 (1)Å, Co-Co 2.492(1)Å] which is bicapped by the sulphido and thiocarboxamido ligands. The cobalt atoms are each ligated by two terminal carbonyl groups, while the tungsten atom is co-ordinated by a diethyldithiocarbamato ligand and a non-bridging diphenylacetylene ligand. Carbon-13 n.m.r. spectroscopic studies confirm that the alkyne is acting as a four-electron donor and undergoes a fluxional process in solution which averages the two ends of the bound alkyne at room temperature. The activation energy for alkyne rotation has been determined to be 60 ± 2 kJ mol^–1 and the process has been modelled by extended-Hückel molecular-orbital calculations.