Selective oxidative carbonylation of amines to oxamides and ureas catalyzed by palladium complexes

A new process for converting secondary airlines into N, N, N', N'-tetraalkyloxamides under CO pressure, catalyzed by homogeneous palladium complexes in the presence of 1,4-dichloro-2-butene (DCB) as an oxidant, has been developed. The mechanism of the oxidative double-carbonylation process, consisting of the oxidation of Pd(0) to Pd(II) with DCB through a beta-chloride elimination of the eta(3)-(chloromethyl)allylpalladium(II) intermediate, the formation of mono- and bis(carbamoyl)palladium species, and a reductive elimination of the two carbamoyl ligands, is proposed based oil studies of the behavior of carbamoylpalladium complexes. When primary amines are employed with DCB as the oxidant. N', N'-dialkyloxamide, is catalytically produced, whereas Urea is exclusively produced when iodine is used as the oxidant. The reaction of an N-monopropylcarbamoylpalladium complex with propylamine under CO gave N, N, N'-dipropylurea. whereas a treatment with diethylamine yielded unsymmetrical N, N-diethyl-N'-propylurea, implying the intermediate formation of propyl isocyanate that is converted into the Urea upon a reaction with the added amine. A kinetic Study on the reaction of chloro-N-propylcarbamoylpalladium with triethylamine suggested a process proceeding through a base-promoted deprotonation of the N-monoalkylcarbamoyl ligand to form propyl isocyanate.