Application of new Ru (II) pyridine-based complexes in the partial oxidation of n-octane

Tridentate and bidentate Ru (II) complexes were prepared through reaction of four pyridine-based ligands: pyCH₂N(R)CH₂py {R = propyl, tert-butyl, cyclohexyl and phenyl; py = pyridine} with the [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂ dimer. Crystal structures of the new terdentate Ru (II) complexes [Ru{pyCH₂N(R)CH₂py}C₆H₆](PF₆)₂ (R = C₃H₇ ( 1 ), C (CH₃)₃ ( 2 ), C₆H₁₁ ( 3 ) and the bidentate Ru (II) complex [Ru{pyCH₂N(R)}C₆H₆]PF₆ (R = C₆H₅ ( 4 )) are reported. It was found that complexes 1, 2 , 3 and 4 crystallised as mono-metallic species, with a piano stool geometry around each Ru centre. All complexes were active in the selective oxidation of n-octane using t-BuOOH and H₂O₂ as oxidants. Complexes 2 and 4 reached a product yield of 12% with t-BuOOH as oxidant, however, superior yields (23–32%) were achieved using H₂O₂ over all systems. The selectivity was predominantly towards alcohols (particularly 2-octanol) over all complexes using t-BuOOH and H₂O₂ after reduction of the formed alkylhydroperoxides in solution by PPh₃. High TONs of up to 2400 were achieved over the Ru/H₂O₂ systems.