Palladium‐catalysed reactions of unsaturated compounds in non‐aqueous solvents: The oligomerization of butadiene using π‐allylpalladium acetate as catalyst

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Abstract
With π‐allylpalladium acetate as catalyst, butadiene is converted in benzene solution into the linear trimer n‐dodecatetraene. Upon addition of triphenyl‐phosphine the linear dimer becomes the main product. In the trimerization the actual catalyst is a C12 H18Pd2OAc2 complex, formed from π‐allylpalladium acetate via (C7H11PdOAc)2 by displacement of the C7 fragments by three butadiene molecules. The displacement takes place via hydrogen transfer, which also explains the catalytic activity of the C12H18Pd2OAc2 complex. When methanol is used as solvent, butadiene is converted into octadienyl, dodecatrienyl or hexadecatetraenyl methyl esters, depending on reaction conditions. In this reaction a complex is formed in which butadiene is coordinated to zerovalent palladium. The consequences of the isolation of the various intermediate complexes in relation to the reaction mechanism are discussed.