Olefin epoxidation catalyzed by [RuIII(TDL)(tmeda)H2O] complexes (TDL = tridentate Schiff-base ligand; tmeda = tetramethylethylenediamine)

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived from condensation of 2-aminophenol or 2-aminobenzoic acid with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde), and tmeda (tetramethylethylenediamine). [RuIII(hpsd)(tmeda)(H2O)]+ (1), [RuIII(hppc)(tmeda)(H2O)]2+ (2), [RuIII(cpsd)(tmeda)(H2O)]+ (3) and [RuIII(cppc)(tmeda)(H2O)]2+ (4) complexes (where hpsd2− = N-(hydroxyphenyl)salicylaldiminato); hppc− = N-(2-hydroxyphenylpyridine-2-carboxaldiminato); cpsd2− = (N-(2-carboxyphenyl)salicylaldiminato); cppc− = N-2-carboxyphenylpyridine-2-carboxaldiminato) were characterized by microanalysis, spectral (IR and UV–vis), conductance, magnetic moment and electrochemical studies. Complexes 1–4 catalyzed the epoxidation of cyclohexene, styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 4-nitrostyrene, cis- and trans-stilbenes effectively at ambient temperature using tert-butylhydroperoxide (t-BuOOH) as terminal oxidant. On the basis of Hammett correlation (log krel vs. σ+) and product analysis, a mechanism involving intermediacy of a [Ru–O–OBut] radicaloid species is proposed for the catalytic epoxidation process.

Mixed-chelate [RuIII(TDL)(tmeda)(H2O)] (TDL = tridentate Schiff-base ligands and tmeda = tetramethylethylenediamine) complexes catalyze the epoxidation of alkenes effectively at ambient temperature using t-BuOOH as terminal oxidant. Based on Hammett correlation (log krelvs. σ+) and product analysis, intermediacy of a [Ru–O–OBut] radicaloid species is proposed for the catalytic epoxidation process.Figure optionsDownload as PowerPoint slide