Synthesis, structural characterization and reactivity of triosmium carbonyl clusters containing oximeligands

Abstract

Reaction of [Os₃(CO)₁₁(NCMe)] with phenyl 2-pyridyl ketoxime produced the clusters [Os₃(CO)₈{μ-η³-ONCPh(NC₅H₄)}₂] 1 and [Os₃H(CO)₁₁{η²-ONCPh(NC₅H₄)}] 2 in 4 and 17% yields, respectively. Oxidative addition of the oximes to the clusters with O–H bond cleavage and the loss of labile acetonitrile groups, and in the case of complex 1 decarbonylation, are observed. Cluster 2 possesses an open linear metal skeleton attached to both the pyridine nitrogen and oximato nitrogen on one terminal Os atom. Heating 2 in refluxing toluene gave [Os₃(μ-H)(CO)₉{µ-η³-ONCPh(NC₅H₄)}] 3 in 13% yield. Treatment of a CH₂Cl₂ solution of [Os₃(CO)₁₀(NCMe)₂] with phenyl 2-pyridyl ketoxime at ambient conditions afforded the bridging oximato clusters 1 and 3 in moderate yields. Cluster 3 and 1 equiv. of phenyl 2-pyridyl ketoxime in refluxing toluene led to conversion to clusters 1 and [Os₃(CO)₈{μ-η³-ONCPh(NC₅H₄)} {μ-η²-N(H)CHPh(NC₅H₄)}] 4 in 12 and 16% yields, respectively. In cluster 4, one of the oximato moieties is deoxygenated with N–O bond cleavage. Treatment of another oxime ligand, benzophenone oxime, with [Os₃(CO)₁₀(NCMe)₂] gave [Os₃(μ-H)(CO)₁₀{μ-η²-ONCPh₂}] 5 in moderate yield. On thermolysis of 5 in toluene, [Os₃(μ-H)₂(CO)₉{μ-η³-ONCPh(C₆H₄)}] 6 and [Os₃(CO)₁₀(μ-OH){μ-NCPh₂}] 7 were isolated in 27 and 21% yields, respectively. The oxime ligand in 6 is converted to a tridentate ligand. In addition to the μ-η²-oximato N–O bridge, the phenyl carbon on the ligand coordinates to the cluster core by ortho-metallation. Cluster 5 isomerizes thermally to 7, which is formed by oxidative addition of the oxime with N–O bond cleavage. A μ₄-oxo hexaosmium cluster, [Os₆(CO)₁₆(μ₄-O){μ-η³-NCPh(C₆H₄)}₂] 8, was isolated in low yield upon refluxing 5 in octane. Vacuum pyrolysis of 5 in 140 °C yielded a pentaosmium carbonyl cluster, [Os₅(CO)₁₅{μ-η³-NCPh(C₆H₄)}] 9. All these clusters have been fully characterized by both spectroscopic and crystallographic techniques.