Pentakis(methoxycarbonyl)cyclopentadiene chemistry. Part 7. Preparation and characterisation of some ruthenium complexes crystal and molecular structure of η-cyclopentadienyl[η-1,2,3,4,5-pentakis(methoxycarbonyl)cyclopentadienyl]ruthenium, [Ru(η-C5H5){η-C5(CO2Me)5}]

Abstract

The salt Tl[C₅(CO₂Me)₅] reacts with [RuCl(PPh₃)₂(η-C₅H₅)] in acetonitrile to give the complex [Ru(NCMe)(PPh₃)₂(η-C₅H₅)][C₅(CO₂Me)₅]; in air the reaction affords [Ru(η-C₅H₅){η-C₅(CO₂Me)₅}]. The crystal structure of the latter has been determined by single-crystal X-ray diffraction methods at 295 K, being refined to a residual of 0.026 for 6 438 ‘ observed ’ reflections. Crystals are triclinic, space group P, with a= 15.790(5), b= 8.968(4), c= 7.947(3)Å, α= 67.52(3), β= 89.52(3), γ= 80.90(3)°, and Z= 2. Both ligands have an η⁵ relationship to the ruthenium in what is essentially an eclipsed sandwich compound. For the C₅H₅ ring, Ru–C is 2.178(2)–2.186(3)Å, while for the C₅(CO₂Me)₅ ligand, Ru–C is 2.157(2)–2.178(2)Å; although these distances are uncorrected for libration, their relativity seems valid. The C₅(CO₂Me)₅ ligand is displaced in reactions with tertiary phosphines in nitrite solvents, and this reaction forms the basis of a process for the oxidation of PPh₃ catalysed by the metallocene. The protonation of [RuH(PPh₃)₂(η-C₅H₅)] by HC₅(CO₂Me)₅ is also described.