Crystal structures of two diruthenium carbonyl complexes derived from cyclo-octatetraene, [Ru2(C8H8SiMe2CH2CH2SiMe2)(CO)5] and [Ru2(C8H8SiMe3)(SiMe3)(CO)4]

Abstract

Cyclo-octatetraene reacts with the complex [Ru(SiMe₂CH₂CH₂SiMe₂)(CO)₄] to give, as one product, the species [Ru₂(C₈H₈SiMe₂CH₂CH₂SiMe₂)(CO)₅](5). An X-ray diffraction study shows that the bonding between the C₈ ring and the two ruthenium atoms is of a novel symmetrical kind comprising a central interannular π-allyl moiety and two ethylenic bonds. The carbonyl ligands are symmetrically related to the mirror plane of the C₈ ring [structure (5) in text]. Crystals of (5) are triclinic, with Z= 2 in a unit cell with dimensions a= 11.851 (2), b= 8.761 (2), c= 11.864(2)Å, α= 100.54(2), β= 110.37(1), γ= 92.25(1)°, and space group P1. The structure has been solved by heavy atom methods from 4 347 intensities [I> 1.75σ(I)] measured on a four-circle diffractometer and refined to R 0.046. The complex [Ru₂(C₈H₈SiMe₃)(SiMe₃)(CO)₄](7) is formed by thermolysis of [Ru₂(C₈H₈SiMe₃)(SiMe₃)(CO)₅](6), a high-yield product of treating [Ru(C₈H₈SiMe₃)(SiMe₃)(CO)₂] with [Ru₃(CO)₁₂], and which is believed, on spectroscopic grounds, to have a structure closely similar to that of (5) as far as the mode of attachment of the ring to the metal carbonyl spine is concerned. An X-ray study of (7) shows that a novel ring-opening raction has occurred; although the spinal sequence Me₃SiRu(CO)₂Ru(CO)₂ of the precursor is retained, the two Ru(CO)₂ units are now twisted relative to one another and the C₈ ring has opened to form a contorted chain, σ-bonded to one Ru atom at one end and to the terminal SiMe₃ group at the other [structure (7) in text]. Crystals of (7) are triclinic, with Z= 2 in a unit cell with dimensions a= 6.903(3), b= 7.669(3), c= 24.454(10)Å, α= 92.41(3), β= 89.87(3), γ= 116.45(3)°, and space group P1. The structure has been solved by heavy-atom methods from 3 485 intensities [I > 1.75σ(I)], and refined to R 0.055.