Decamethylosmocene-catalyzed efficient oxidation of saturated and aromatic hydrocarbons and alcohols with hydrogen peroxide in the presence of pyridine

摘要

Decamethylosmocene, (Me_5C_5)_2Os (1), is a pre-catalyst in a very efficient oxidation of alkanes with hydrogen peroxide in acetonitrile at 20-60 °C. The reaction proceeds with a substantial lag period that can be reduced by the addition of pyridine in a small concentration. The lag period can be removed if 1 is incubated with pyridine and/or H _2O_2 in MeCN prior to the alkane oxidation. Alkanes, RH, are oxidized primarily to the corresponding alkyl hydroperoxides, ROOH. Turnover numbers attain 51,000 in the case of cyclohexane (maximum turnover frequency was 6000 h~(-1)) and 3600 in the case of ethane. The oxidation of benzene and styrene also occurs with a lag period to afford phenol and benzaldehyde, respectively. A kinetic study of cyclohexane oxidation and selectivity parameters (measured in the oxidation of n-heptane, methylcyclohexane, isooctane, cis- and trans-dimethylcyclohexanes) indicates that the oxidation of saturated, olefinic, and aromatic hydrocarbons proceeds with the participation of hydroxyl radicals. The 1/H_2O _2/py/MeCN system also oxidizes 1-phenylethanol to acetophenone.