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 -[(η 6 -C 6 H 6 )Ru( L )][PF 6 ][X] ( 1 − 6; X = PF 6 or Cl), formed by reacting 2-MeSC 6 H 4 CH═NCH 2 CH 2 E-C 6 H 4 -4−R ( L1 − L3 ) and 2-MeSC 6 H 4 CH 2 -NHCH 2 CH 2 E-C 6 H 4 -4−R ( L4 − L6 ) (where E = S or Se, R = H; E = Te, R = OMe) with [{(η 6 -C 6 H 6 )RuCl(μ-Cl)} 2 ] and NH 4 PF 6, have been characterized by 1 H, 13 C{ 1 H}, 77 Se{ 1 H}, and 125 Te{ 1 H} 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, t BuOOH, NaOCl, and NaIO 4 and transfer hydrogenation reaction of ketones with 2-propanol. The TON values are up to 9.9 × 10 4 and 9.8 × 10 4 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.