Incorporation of CO2 in Butadiene Dimerization Catalyzed by Palladium Complexes. Formation of 2-Ethylidene-5-hepten-4-olide

Abstract Reaction of carbon dioxide with butadiene catalyzed by palladium–phosphine complexes was studied. When the reaction was carried out in certain polar, aprotic solvents, such as dimethylformamide (DMF), 2-ethylidene-5-hepten-4-olide was formed in about 5% yield by the incorporation of CO2 together with the formation of butadiene linear dimers. The main dimer was 1,3,7-octatriene. The ditertiary phosphines, R2PCH2CH2CH2PR2 where R is methyl or phenyl, were found to be suitable as the ligand for the olide synthesis. A possible mechanism involving the intermediate of π-allyl, σ-allyl form from two moles of butadiene and the palladium complex is proposed.