[PdCl2(PPh3)2]-PPh3, in the presence of NEt3, is moderately active in the ethoxycarbonylation of 2-- chlorocyclohexanone to the -ketoester (ca. 140 TON in 4 h at 100°C, 100 atm, P/Pd=2.5, [Pd]=5×10-3 mol l-1, NEt3/substrate=1.2). The yield increases upon increasing pCO, passes for a max. when the P/Pd molar ratio is 2.5 and it is approx. of the first order with respect to the concn. of the substrate. A reaction mechanism is proposed, which involves the oxidative addn. of the chloride to a Pd(0) species, CO insertion forming a Pd(II) -keto-acyl complex, nucleophilic attack of ethanol to the carbon atom of the acyl moiety and HCl elimination to regenerate the starting Pd(0) species. When the carbonylation is attempted in the presence of H2O and in the absence of NEt3, in place of the expected carbonylation product, there is hydrogen transfer from the system H2O-CO to the org. substrate with hydrogenolysis of the C-Cl bond. For the hydrodechlorination reaction it is proposed that, after the oxidative addn. step to a Pd(0) complex, the Pd-C bond of the alkyl intermediate is protonolyzed by the acid that forms during the course of the reaction and that the Pd(II) complex is then reduced by CO in the presence of H2O.
PdCl2(PPh3)2]-PPh3 catalyzed regiospecific alkoxycarbonylation of --chlorocyclohexanone to -keto esters
TONIOLO, Luigi
1999-01-01
Abstract
[PdCl2(PPh3)2]-PPh3, in the presence of NEt3, is moderately active in the ethoxycarbonylation of 2-- chlorocyclohexanone to the -ketoester (ca. 140 TON in 4 h at 100°C, 100 atm, P/Pd=2.5, [Pd]=5×10-3 mol l-1, NEt3/substrate=1.2). The yield increases upon increasing pCO, passes for a max. when the P/Pd molar ratio is 2.5 and it is approx. of the first order with respect to the concn. of the substrate. A reaction mechanism is proposed, which involves the oxidative addn. of the chloride to a Pd(0) species, CO insertion forming a Pd(II) -keto-acyl complex, nucleophilic attack of ethanol to the carbon atom of the acyl moiety and HCl elimination to regenerate the starting Pd(0) species. When the carbonylation is attempted in the presence of H2O and in the absence of NEt3, in place of the expected carbonylation product, there is hydrogen transfer from the system H2O-CO to the org. substrate with hydrogenolysis of the C-Cl bond. For the hydrodechlorination reaction it is proposed that, after the oxidative addn. step to a Pd(0) complex, the Pd-C bond of the alkyl intermediate is protonolyzed by the acid that forms during the course of the reaction and that the Pd(II) complex is then reduced by CO in the presence of H2O.
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