Selective Palladium(II)-Catalyzed Dimerization of Styrenes and Acrylates in Molten Tetrabutylammonium Acetate as an Ionic Liquid

A method for the selective dimerization of styrenes and acrylates has been developed. The reaction is catalyzed by a very low amount of palladium acetate in molten tetrabutylammonium acetate without the need for any additional ligand. The use of this method enabled the coupling of substituted vinyl arenes in reasonable yields to give exclusively the (E,E)-1,4-diarylbutadiene motif within 7-10 h. Acrylates, on the other hand, exhibit higher reactivity, and the use of dibutyl acrylate resulted in the quantitative synthesis of dibutyl 2-methyleneglutarate in less than 2 h. This selectivity is unprecedented in the literature. The role of the ionic liquid and the different catalytic pathways involved in the two processes were also elucidated. The selective dimerization of styrenes and acrylates was possible with a very low amount of palladium acetate in molten tetrabutylammonium acetate. The coupling of substituted vinyl arenes gave exclusively the (E,E)-1,4-diarylbutadiene motif within 7-10 h, whereas butyl acrylate was converted into dibutyl 2-methyleneglutarate in less than 2 h. The catalytic pathways involved in the two processes were elucidated along with the role of the ionic liquid. image