Hydrocarbon complexes of iron, ruthenium, and osmium. Part 11. Diruthenium complexes of pentalene derived from cyclo-octatetraene: crystal and molecular structure of the fluxional molecule dicarbonyl(trimethylsilyl)(1—3:6—7-η-8-endo-trimethylsilylcyclo-octatrienyl)-ruthenium, a pentalene precursor

Abstract

Cyclo-octatetraenes C₈H₇R(R = H, Me, Ph, or SiMe₃) react with [Ru(SiMe₃)₂(CO)₄] in hexane at reflux to give trimethylsilyl migration products [Ru(SiMe₃)(CO)₂{C₈H₇R(SiMe₃)}] and ring-closed tetrahydropentalenyl complexes [Ru(SiMe₃)(CO)₂{C₈H₈R)}]. The molecular structure of complexes of the former type has been established by a single-crystal X-ray diffraction study of [Ru(SiMe₃)(CO)₂{C₈H₈(SiMe₃)}]. Crystals are triclinic, space group P with Z= 2 in a unit cell of dimensions: a= 9.972(3), b= 16.082(6), c= 6.662(2)Åα= 89.46(2), β=110.44(2). and γ= 82.46 (2)°. The structure has been determined by heavy-atom methods from diffractometer data and refined to R 0.035 for 3 146 independent reflections The results establish that one SiMe₃ group is bonded to ruthenium and one to the C₈ ring. The hydrocarbon ligand is co-ordinated to the ruthenium through η³-ally1 and η²-ethylenic interactions within a C₈ ring, with another ethylenic bond unco-ordinated. The complex exhibits luxional behaviour in solution, which has been investigated by variable-temperature ¹H and ¹³C n.m.r. spectroscopy. Heating cyclo-octatetraenes C₈H₇R with [Ru(SiMe₃)₂(CO)₄] in heptane, or heating [Ru(SiMe₃)(CO)₂{C₈H₇R(SiMe₃)}] directly in heptane or octane, effects ring closure with ejection of the C-bonded SiMe₃ group, producing diruthenium pentalene complexes [Ru₂(SiMe₃)₂(CO)₄(C₈H₅R)] in moderate yield. Under mild conditions (hexanereflux)[Ru(GeMe₃)₂(CO)₄] with cyclo-octatetraene yields small amounts of [Ru(GeMe₃)(CO)₂{C₈H₈(GeMe₃)}] whereas [Ru(SiMe₃)(GeMe₃)(CO)₄] readily gives [Ru(GeMe₃)(CO)₂{C₈H₈(SiMe₃)}]. In heptane or octane [Ru(GeMe₃)₂(CO)₄] undergoes more complex reactions, affording [Ru(GeMe₃)(CO)₂(C₈H₉)], [Ru₂(GeMe₃)₂(CO)₄(C₈H₈)], and [Ru₂(GeMe₃)₂(CO)₄(C₈H₆)]. The mechanism of pentalene-ruthenium complex formation is discussed.