The effects of the solvent and the ligand chirality on the regioselectivity of alkene oxidative esterification by PdII carboxylates |
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Authors: | Kozitsyna N Yu Martens M V Stolyarov I P Gekhman A E Vargaftik M N Moiseev I I |
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Institution: | (1) N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky prosp., 117907 Moscow, Russian Federation |
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Abstract: | The effects of the solvent and the ligand chirality on the regioselectivity of oxidative esterification of propylene and cyclohexene
by PdII carboxylates were studied using achiral (MeCO2
−, Me2CHCH2CO2
−), racemic ((±)-CF3CF2CF2OC*F(CF3)CO2
−), and chiral ((S)−(+)−MeC*H(Et)CO2
−, (+)−CF3CF2CF2OC*F(CF3)CO2
−) carboxylate ligands. The oxidation of alkenes in aprotic media (CHCl3, CH2Cl2, CO2, THF) affords mainly allylic esters (in the case of cyclohexene also homoallylic esters) and the oxidative esterification
at the vinylic position is absent. In weakly solvating media (CHCl3, CH2Cl2) the regioselectivity of cyclohexene oxidation (the allyl to homoallyl ratio) increases substantially on going from achiral
or racemic acido ligands to chiral acido ligands. In a more donor medium (THF) the ligand chirality effect almost vanishes.
The effects of the ligand chirality and the nature of the solvent on the mechanism of alkene oxidation by PdII complexes are discussed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1695–1703, September, 1999. |
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Keywords: | palladium alkenes π -complexes σ -complexes oxidative esterification regioselectivity solvent effects chiral ligands |
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