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The dinuclear osmium(I) compound [Os2(MeCO2)2(CO)6] has labile axial CO ligands and there is no evidence for equatorial substitution in its reactions. Refluxing tetrahydrofuran (thf) gives [Os2(MeCO2)2(CO)5(thf)] which reacts with tertiary phosphines to give [Os2(MeCO2)2(CO)5L](L = PPh3 or PMe2Ph) and with [N(PPh3)2]Cl to give [N(PPh3)2][Os2(MeCO2)2Cl(CO)5], the X-ray crystal structure of which confirms axial substitution. Direct reaction of [Os2(MeCO2)2(CO)6] with tertiary phosphines, pyridine, or acetonitrile ligands, L, gives the di-axially substituted compounds [Os2(MeCO2)2(CO)4L2] and no mono-substituted compounds were observed in most cases. Treatment of the 13CO-enriched compound [Os2(MeCO2)2(CO)6] with acetonitrile gives enriched [Os2(MeCO2)2(CO)4(MeCN)2]. This reacted with natural abundance CO to reform [Os2(MeCO2)2(CO)6] which contains 13CO only in sites cis to the Os–Os bond. Equilibration between these sites and those trans to the Os–Os bond is slow with t½=ca. 6 d at room temperature. |
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