Synthesis and characterisation of neutral and cationic 2,7-dimethyloctadienediylruthenium(IV) complexes. X-Ray crystal structure of cis-bis(acetonitrile)chloro[(1,2,3,6,7,8-η)-2,7-dimethylocta-2,6-diene-1,8-diyl]ruthenium(IV) tetrafluoroborate

Reactions of [{Ru(η3:η3-C10H16)Cl(µ-Cl)}2]1 with the ligands (L) P(OMe)3, ButNC or PriNC in chloroform solution give the complexes [Ru(η3:η3-C10H16)Cl2L]2–4. Treatment of these complexes with Ag[BF4] and additional free ligand in acetone solution gives the salts [Ru(η3:η3-C10H16)ClL2][BF4]5–7. The reaction of 1 with Ag[BF4] in acetonitrile solution yields [Ru(η3 : η3-C10H16)Cl(NCMe)2][BF4]8 which slowly converts in solution into an alternative stereoisomer 9. The structures proposed for 2–9 all feature an approximate trigonal-bipyramidal co-ordination at ruthenium, occupation of two equatorial sites by the η3 : η3-2,7-dimethyloctadienediyl ligand, and a local C2-symmetry configuration for the octadiendiyl chain. In 2–4 it is the two-electron ligand that occupies the third equatorial site with both chlorides axial. In 5–7 the chloride occupies the third equatorial site and both the two-electron ligands are axial. For the two acetonitrile-containing stereoisomers, the chloride is axial in 8 and equatorial in 9. An equilibrium 8⇌9 exists in acetonitrile solution with K298= 30 ± 5, K298(forward)=(7.6 ± 0.6)× 10–6 s–1, ΔH‡= 123 ± 3 kJ mol–1, ΔS‡= 68 ± 9 J K–1 mol–1, as determined by 1H NMR spectroscopy and sampling techniques. The structure of 8 has been confirmed by X-ray diffraction: space group P with a= 7.80(1), b= 15.69(1), c= 7.63(1)A, α= 96.5(1), β= 87.1(1), γ= 96.9(1)° and Z= 2. The structure was refined to R= 0.082 for 1766 unique reflections.