Transfer Hydrogenation of Ketones and Catalytic Oxidation of Alcohols with Half-Sandwich Complexes of Ruthenium(II) Designed Using Benzene and Tridentate (S, N, E) Type Ligands (E = S, Se, Te)

The complexes of composition fac-[(η⁶-C₆H₆)Ru(L)][PF₆][X] (1−6; X = PF₆ or Cl), formed by reacting 2-MeSC₆H₄CHNCH₂CH₂E-C₆H₄-4−R (L1−L3) and 2-MeSC₆H₄CH₂-NHCH₂CH₂E-C₆H₄-4−R (L4−L6) (where E = S or Se, R = H; E = Te, R = OMe) with [{(η⁶-C₆H₆)RuCl(μ-Cl)}₂] and NH₄PF₆, have been characterized by ¹H, ¹³C{¹H}, ⁷⁷Se{¹H}, and ¹²⁵Te{¹H} NMR spectroscopy and X-ray crystallography. The Ru−Se and Ru−Te bond lengths are in the ranges 2.4837(14)−2.4848(14) and 2.6234(6)−2.6333(7) Å, respectively. Complexes 1−6 have been found to be efficient catalysts for catalytic oxidation of alcohols with N-methylmorpholine-N-oxide, tBuOOH, NaOCl, and NaIO₄ and transfer hydrogenation reaction of ketones with 2-propanol. The TON values are up to 9.9 × 10⁴ and 9.8 × 10⁴ for two catalytic processes, respectively. The oxidation probably involves the formation of intermediate species having Ru(IV)O. Complexes 1−3 are as efficient as 4−6 for transfer hydrogenation of ketones. In transfer hydrogenation, the mechanism does not appear to be dependent on the availability of hydrogen on nitrogen and probably involves Ru−H bond formation. The catalytic efficiency for both processes follows the order Te > Se > S, which may be due to the presence of a MeO group on Te.