Piano-Stool Complexes of Ruthenium(II) Designed with Arenes and N-[2-(Arylchalcogeno)ethyl]morpholines: Highly Active Catalysts for the Oxidation of Alcohols with N-Methylmorpholine N-Oxide, tert-Butyl Hydroperoxide and Sodium Periodate and Oxychloride

The reactions of [{(eta(6)-C(6)H(6))RuCl(mu-Cl)}(2)] and [{(eta(6)-p-cymene)-RuCl(mu-Cl)}(2)] with N-[2-(arylchalcogeno)ethyl]morpholines (L) (aryl = Ph/2-pyridyl for S, Ph for Se, 4-MeOC(6)H(4) for Te) and NH(4)PF(6) result in piano-stool complexes of Ru(II) of composition [RuCl(eta(6)-C(6)H(6))(L)][PF(6)]/[RuCl(eta(6)-p-cymene)(L)]-[PF(6)], which give characteristic (1)H, (13)C{(1)H}, (77)Se{(1)H}, and (125)Te{(1)H} NMR spectra. Some of them have also been characterized by X-ray crystallography [Ru-S, Ru-Se, and Ru-Te bond lengths: 2.3815(12)/2.3742(14), 2.4837(14), and 2.6143(7) angstrom, respectively]. The cyclic voltammograms show that all the complexes undergo irreversible oxidation (E(1/2) = 0.290-0.586 V). All the ruthenium complexes have been explored for their catalytic activity in the oxidation of primary and secondary alcohols with N-methylmorpholine N-oxide (NMO), tBuOOH, NaOCl, and NaIO(4) (TON values upto 9.8 x 10(4)). The efficiency of the catalytic oxidation reaction decreases in the order Te > Se > S. The intermediate species involved in the oxidation reactions appear to incorporate the Ru(IV)=O group.