Tetranuclear tungsten cyclooctatetraenyl alkoxides [W2COT(OR)4]2, where R=Me, Et and Pr

Two equivalents of W2COT(NMe2)4 react with eight equivalents of methanol, ethanol, or n-propanol to form the corresponding tetranuclear alkoxide clusters: [W2COT(OR)4]2 where R=Me, Et, or Pr. Single-crystal X-ray diffraction studies on the ethoxide and propoxide compounds reveal centrosymmetric molecules containing two [W2(μ-η5,η5-COT)(μ-OR)(OR)2] fragments. Each fragment has a W–W bond length of ca. 2.39 Å and is connected to the other by a pair of symmetrically-bridging alkoxides. These bridging alkoxides are not cleaved in the presence of σ-donors thf and pyridine, or π-acceptor 2-butyne. NMR data suggest that this structure is maintained in solution. Unlike in the related dinuclear alkoxides, W2COT(OR)4 [where R=CH2But, Pri and But], the COT ligands are not fluxional at ambient temperature. The structural similarities between [W2COT(OPr)4]2, W2COT(OBut)4, and W4(H)2(OPri)14 are discussed.