Selective cis-dihydroxylation of olefins using recyclable homogeneous molybdenum acetylide catalyst

Selective cis-dihydroxylation of various olefins has been carried out using molybdenum acetylide complex CpMo(CO)3(CCPh) (1) as catalyst and hydrogen peroxide as an efficient and environmentally benign oxidant. In case of cyclohexene, very high conversion (95%) and selectivity (86%) for cis-dihydroxylated product has been achieved using H2O2 as an oxidant and t-butanol as a solvent. cis-Dihydroxylation of other substrates like styrene, α-methyl styrene, limonene and cyclopentene has also been carried out with very high selectivity for diol. The catalyst and intermediate species have been characterized using FT-IR, UV–vis spectral analysis and XPS studies as well as cyclic voltametric studies. These studies suggest that molybdenum oxo–peroxo complex is the catalytically active species. The intermediate blue complex when characterized by ESI MS suggested the formation of dimeric molybdenum complex and XPS and cyclic voltametric studies confirm the presence of mixed valence Mo(V) and Mo(VI) in the reaction intermediate. Based on the characterization results possible mechanism for dihydroxylation is proposed. Interestingly, even though the catalyst is homogeneous; it could be recovered quantitatively by extraction in aqueous phase and recycled five times without any appreciable loss in cyclohexene conversion and selectivity for cis-1,2-cyclohexanediol.

Selective cis-dihydroxylation of various olefins using molybdenum acetylide complex CpMo(CO)3(CCPh) as efficient and recyclabale catalyst with H2O2 as oxidant has been reported. The extensive characterization of catalyst and intermediate species suggest molybdenum oxo–peroxo complex to be catalytically active species and formation of dimeric molybdenum complex with mixed valence Mo(V) and Mo(VI) as reaction intermediate. Based on the characterization results possible mechanism is proposed.Figure optionsDownload as PowerPoint slide