Chemistry of Tetraosmium Carbonyl Clusters with Phenylazopyridine Ligands: Synthesis, Structure and Electrochemistry

Two new tetraosmium carbonyl clusters [Os4(μ-H)4(CO)11{η1-NC5H4(N=N) C6H5}] (1) and [Os4(μ-H)4(CO)10{η2-NC5H4(N = N)C6H5}] (2) were synthesized from the reaction of [Os4(μ-H)4(CO)12] with two equivalent of 2-phenylazopyridine ligand in dichloromethane at ambient temperature using trimethylamine-N-oxide as the decarbonylation reagent. Subsequent chromatographic purification led to the isolation of 1 and 2 as stable orange and blue solids in respectively 25 and 13% yields. Complex 1 converted to 2 in a 25% yield in refluxing chloroform. Treating a solution of [Os4(μ-H)4(CO)12] in dichloromethane with two equivalent of 3-phenylazopyridine led to the formation of another two new clusters [Os4(μ-H)4(CO)11{η1-NC5H4(N = N)C6H5}] (3) and [Os4(μ-H)4(CO)10(NMe3){η1-NC5H4(N=N)C6H5}] (4), which could be isolated as yellow solids in 34% and 21% yields respectively. Thermolysis of 3 or 4 in refluxing n-hexane gives [Os4(μ-H)3(CO)10{μ-η3-NC5H3(N=N)C6H5}] (5) in 24 and 33% yields respectively. Their electronic absorption properties and electrochemical behavior are also reported.