Synthesis, structural characterization and reactivity of triosmium carbonyl clusters containing oxime ligands

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.