Addition of diphenyl diselenide (PhSeSePh) to the clusters [Os3(CO)10(μ-dppm)] and [(μ-H)Os3(CO)8{Ph2PCH2P(Ph)C6H4}]: X-ray structures of [Os2(CO)4(μ-SePh)2(μ-dppm)], [Os3(CO)6(μ-CO)(μ-Se)2(μ-C6H4)(μ-dppm)] and two isomers of [Os3(CO)8(μ-SePh)2(μ-dppm)]

The reaction of [Os3(CO)10(μ-dppm)] (4) with diphenyldiselenide in refluxing toluene at 110 °C affords the dinuclear compound [Os2(CO)4(μ-SePh)2(μ-dppm)] (5), three 50 electron isomeric triosmium compounds 6, 7 and 8 with the formula [Os3(CO)8(μ-SePh)2(μ-dppm)], two triosmium benzyne compounds [Os3(CO)6(μ-CO)(μ-η2-Se)2(μ-C6H4)(μ-dppm)] (9) and [Os3(CO)9(μ-SePh)2(μ-η2-C6H4)(μ-dppm)] (10) in 11%, 19%, 15%, 5%, 18% and 6% yields, respectively. Thermolysis of both 6 and 8 in refluxing toluene gives the dinuclear compound 5 in moderate yield, whereas a similar thermolysis of 7 yields 5 and 9 in 20% and 27% yields, respectively. Compound 10 converts to 9 refluxing in octane. Treatment of the unsaturated compound [(μ-H)Os3(CO)8{Ph2PCH2P(Ph)C6H4}] (11) with diphenyldiselenide in refluxing benzene gives 5, 6, 7 and 8 in 8%, 20%, 25% and 10% yields, respectively. The molecular structures of 5, 6, 7 and 9 have been determined by single crystal X-ray diffraction studies. The molecular structure of 5 shows classical “sawhorse” structure with two bridging phenylselenido ligands as well as a dppm ligand. The solid-state structure of 6 reveals that two SePh groups span the open Os–Os edges of the Os3 triangle, while the dppm ligand bridges one of the closed Os–Os edges. In compound 7, one SePh spans the open Os–Os site, while the other spans one of the two closed Os–Os edges and the dppm ligand bridges the third Os–Os vector. Compound 9, which exists as a mixture of two isomers in solution, contains two triply bridging selenido ligands and a benzyne ligand, which are believed to have been formed by the cleavage of Se–Se bond of the PhSeSePh ligand followed by C–Se and C–H activation of the SePh group. The 54 electron compound 10 has been characterized by elemental analysis, IR, 1H NMR, 31P{1H} NMR and mass spectroscopic data.