Chelate and Bridge Diphosphine Isomerization: Triosmium and Triruthenium Clusters Containing 1,1‘-Bis(diphenylphosphino)ferrocene (dppf)

The coordination mode of dppf {dppf = 1,1‘-bis(diphenylphosphino)ferrocene} at triosmium and triruthenium carbonyl clusters has been studied. Heating [Os3(CO)12] with dppf in the presence of Me3NO in benzene at 60 °C furnishes three triosmium compounds, [Os3(CO)11(κ1-dppf)] (1), [Os3(CO)10(κ2-dppf)] (2), and [Os3(CO)10(μ-dppf)] (3) in 10, 20, and 30% yields, respectively. Reaction of the labile cluster [Os3(CO)10(MeCN)2] with dppf at room temperature also gives 1, 2, and 3 (5, 10, and 35% yields). Treatment of 1, which contains a pendant diphosphine, with Me3NO at room temperature affords 2 via a ring closure reaction, whereas heating 2, in which the dppf ligand is chelating, at 110 °C affords the thermodynamically stable bridging isomer 3, in which phosphorus atoms are bound at equatorial positions. Reaction of the unsaturated cluster [Os3(CO)10(μ-H)2] (4) with dppf in refluxing THF affords the bridging complex [Os3(CO)8(μ-dppf)(μ-H)2] (6) in high yield as the sole product. Hydrogenation of 3 with H2 at 110 °C at 1 atm also yields 6. Reactions of both the saturated [Os3(CO)10(μ-dppm)] (7) and electron-deficient [Os3(CO)8{μ3-Ph2PCH2P(Ph)C6H4}(μ-H)] (8) with dppf at 110 °C and at room temperature respectively yield [Os3(CO)9(μ-dppm)(κ1-dppf)] (9) and [Os3(CO)8(μ-dppm)(κ2-dppf)] (10). Compound 9 converts to 10 at 110 °C via CO loss and phosphorus coordination. Reaction of [Ru3(CO)12] with dppf in the presence of Me3NO affords the dihydroxy-bridged complex, [Ru3(CO)8(μ-dppf)(μ-OH)2] (13), together with the previously reported compounds [Ru3(CO)10(μ-dppf)] (11) and [Ru3(CO)8(μ-dppf)2] (12).