CATALYTIC HYDRATION OF DIETHYL MALEATE TO DIETHYL MALATE USING DIVALENT COMPLEXES OF PALLADIUM(II) AS CATALYSTS

The complexes [Pd(mu-OH)(L-L)]2(2+) (L-L = dppe, dcpe) act as catalysts in aqueous THF solution for the addition of water to the carbon-carbon double bond of diethyl maleate to give the alcohol, diethyl malate. This addition reaction of diethyl maleate to give diethyl malate, as well as its oxidation to diethyl oxaloacetate, is catalyzed in aqueous THF solution by a mixture of PdCl42- and CuCl2. Isomerization of diethyl maleate to diethyl fumarate, along with hydrolysis products of each alkene, is also observed with both catalyst systems. Mechanisms for these palladium(II) catalyzed reactions involving the protonolysis of an intermediate alkylpalladium complex are proposed. In aqueous solution, tertiary phosphines catalyze the cis-trans isomerization of diethyl maleate to diethyl fumarate.