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)

Abstract

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)Å, 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)Å] 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).