Hydrocarbon complexes of iron, ruthenium, and osmium. Part VIII. Isolation of η-(1,1,1-tricarbonyl-1-metallainden-1-yl) tricarbonylmetal-(M–M)[M = iron, ruthenium, or osmium] complexes: crystal and molecular structure of η-(1,1,1-tricarbony-1-osmainden-1-yl)tricarbonylosmium (Os–Os)

Treatment of [Os(MMe3)2(CO)4](M = Si or Ge) or [{Os(SiMe3)(CO)4}2] with cyclo-octatetraene (COT) gives primarily the 1,2,3,3a,6a-η-1,4,5,6-tetrahydropentalenyl complexes [Os(MMe3)(CO)2(C8H9)], with minor formation of [Os2(CO)6(C8H10)] and of complexes of unidentified dimers of COT, [Os(CO)2(C16 H16)] and [Os(CO)3(C16 H16)]. The latter is also formed on heating [Os3(CO)12] with COT in octane. Under u.v. irradiation a moderate yield of [Os(CO)3(C8H8)] is obtained from [{Os(SiMe3)(CO)4}2] and COT. Dimethyl(tetracarbonyl) osmium and cyclo-octatetraene afford a complicated mixture from which η-(1,1,1-tricarbonyl-1-osmainden-1-yl)tricarbonylosmium (Os–Os), [Os2(CO)6(C8H6)], was obtained and characterised by X-ray diffraction. Crystals are triclinic(P) with two molecules per unit cell [a= 7.973(4), b= 10.684(4), c= 9.191(3)A, α= 89.16(3), β= 99.28(3), γ= 91.75(3)°]. The structure was solved by conventional heavy-atom methods from 2 152 independent reflections and refined to R= 0.053 (R′= 0.064). One osmium atom has been incorporated with the eight carbon atoms of the original cyclo-octatetraene ring to form a planar osmaindenyl system. The second osmium atom is bonded to the first [Os–Os = 2.754(2)A] and is also η4-bonded to the four carbon atoms of the 5-membered ring, thereby achieving octahedral co-ordination.Debromination of 1,4-dibromocyclo-octatetraene with [Fe2(CO)9] or [Fe(CO)4]2– affords benzocyclobutadiene-(tricarbonyl)iron. In refluxing hydrocarbons. [Fe2(CO)9] or [Ru3(CO)12] and 1,4-dibromocyclo-octacetraene yield the metallainden-1-yl complexes [M2(CO)6(C8H6)](M = Fe or Ru).