“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 [{(η 6 ‐C 6 H 6 )RuCl(μ‐Cl)} 2 ] and [{(η 6 ‐ p ‐cymene)RuCl(μ ‐ 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(η 6 ‐C 6 H 6 )(L)][PF 6 ]/[RuCl(η 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) Å, respectively]. The cyclic voltammograms show that all the complexes undergo irreversible oxidation ( E ${1 \over 2}$ = 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), t BuOOH, NaOCl, and NaIO 4 (TON values upto 9.8 × 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.