Synthesis, Characterization, and Crystal Structures of a Series of Osmium-Rhodium Mixed-Metal Carbonyl Clusters: [N(PPh₃)₂][Os₆Rh(μ-H)₂(CO) ₂₀], [Os₆Rh(μ-H)₇(μ-CO)(CO)₁₈], [Os₆Rh(μ-H)₉(CO)₁₈]

The reaction between [N(PPh3)2][Os3(μ-H)(CO)11] and [Rh(COD)2][SbF6] (COD = cycloocta-1,5-diene) yields the known cluster [Os3Rh(μ-H)3(CO)10(COD)] (1) and the new complex [N(PPh3)2][Os6Rh(μ-H)2(CO) 20] (2). Subsequent reaction of 1 with CO gas in CH2Cl2 produces [Os3Rh(μ-H)3(CO)12] (4). Compound 1 also reacts with 1 equiv of [N(PPh3)2][Os3(μ-H)(CO)11] to give 2. Hydrogenation of 1 results in the hydrogen-rich cluster [Os6Rh(μ-H)9(CO)18] (5) in moderate yield. Reaction of 1 with diphenylacetylene affords [Os3Rh(μ-CO)(CO)9(μ4-η 2-PhC2-Ph)(μ2-η1:η 2-PhC2PhH)] (6). On the other hand, the unsaturated cluster [Os3(μ-H)2(CO)10] reacts with [Rh(dppm)2][BF4] (dppm = bis(diphenylphosphino)methane) to give [Os6Rh(μ-H)7(μ-CO)(CO)18] (3) in good yield. The crystal structures of 2, 3, 5, and 6 were determined. Clusters, 2, 3, and 5 consist of a central rhodium atom linking two triosmium units; however, the rhodium atom of 2 bridges two triosmium units, while 3 and 5 possess a sandwich-type structure. Complex 6 has a butterfly arrangement of three osmium atoms and one rhodium atom which contains a diphenylacetylene fragment in a μ4-η2 arrangement and an alkenyl group in a μ2-η1:η2 configuration.