Affiliation:
1. Department of Chemistry, Jadavpur University, Kolkata - 700 032, India
Abstract
Arylazoimidazole brings azoimine (-N=N-C=N-) chelating N(azo), N(imine) (abbreviated
- N, N/) centres and forms Ru(II) and Os(II) carbonyl complexes. These complexes act as catalysts
for the oxidation of alcohols to aldehydes/ketones by tertiary butyl hydro peroxide (ButOOH), hydrogen
peroxide (H2O2) and N-methylmorpholine-N-oxide (NMO) as oxygen sources. Different substituted
arylazoimidazoles such as 1-alkyl-2-(arylazo)imidazoles (RaaiR/), 1-alkyl-2-(naphthyl-α/β-
azo)imidazoles (α/β-NaiR) and (1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole, SRaaiNR/) are used to
prepare Ru/Os-CO complexes. Ancillary ligands like hydride (H-), chloride (Cl-), triphenylphosphine
(PPh3) are used to monitor the catalytic efficiency of the complexes. Aromatic and aliphatic alcohols
like benzyl alcohol, 2-butanol, cyclopentanol, cyclohexanol, 1-phenylethanol, cinnamyl alcohol, diphenylmethanol,
are oxidized to the corresponding benzaldehyde, 2-butanone, cyclopentanone, cyclohexanone,
phenylacetone, cinamaldehyde, cyclopentanone, benzophenone, respectively. Different
physicochemical analyses (FT-IR, UV-Vis, Mass, NMR) suggest that the complexes react with an
oxidant to yield high valent ruthenium/osmium-oxo species (RuIV=O; OsIV=O), which is capable of
transferring the oxygen atom to alcohols. GC analysis accounts that percentage conversion order is as
follows : Cinnamyl alcohol > Cyclohexanol ~ 1-Phenylethanol > Diphenylmethanol > Cyclopentanol
> 2-Butanol > Benzyl alcohol. The oxidation efficiency of the oxidant follows the order : NMO >
ButOOH > H2O2. RuII complexes are more potent catalysts than OsII complexes. Out of three series
of RuII complexes, [RuCl(CO)(SMeaaiNEt)]ClO4 and [RuCl(CO)(SEtaaiNMe)]ClO4 showed highest
catalytic efficiency amongst 32 catalysts.
Funder
Council of Scientific and Industrial Research (CSIR)
Publisher
Bentham Science Publishers Ltd.
Subject
Organic Chemistry,Analytical Chemistry,Catalysis