Synthesis and structural characterisation of osmium carbonyl clusters containing azo ligands

Treatment of [Os3(CO)10(NCMe)2] (1) with 1-(2-thiazolylazo)-2-naphthol resulted in two new clusters [(μ-H)Os3(CO)10{NC3HS-N=N-C10H6(OH)}] (2) and [(μ-H)Os3(CO)9(μ-η3-NC3H2S(N=N)C10H6(O)] (3) in 30 and 45% yields, respectively. Cluster 2 contains an azo ligand moiety in the usual orthometallated mode. In cluster 3, the O-H bond is cleaved in the azo ligand and acts as a five-electron donor in the triosmium framework. Treatment of 1 with 4-nitro-4′-aminoazobenzene yields only [(μ-H)Os3(CO)10(μ-NHC6H4-N=N-C6H4NO2] (4) (35%) where the nitrogen atom symmetrically bridges the Os-Os bond. In another class of azo ligands, 2-[4-(diethylamino)phenylazo]benzoic acid reacts with 1 to give two complexes [(μ-H)Os3(CO)10(O2CC6H4-N=N-C6H4NEt2)] (5) (50%) and [Os3(CO)9(μ-Cl)(μ-η2-OC(O)C6H4N=NHC6H4NEt2)] (6) (17%). In cluster 5, the ligand is bonded to the metal core through a carboxylate which takes up an axial position; while in cluster 6, the two nonbonded Os atoms are symmetrically bridged by a chloride and by oxygen atom in the azo ligand. Treatment of 1 with 2-[4-(diethylamino)phenylazo]benzoic acid in refluxing THF produced 5 as the sole product. All the complexes 2-6 have been fully characterized in solution by conventional spectroscopic methods and in the solid state by single-crystal X-ray diffraction analysis.