The rates of catalytic dimerization of alkyl acrylates by PdCl2(NCPh)2 and by [(C2H4)RhCl]2 are greatly increased by the combination of a Lewis acid promoter and a proton source. For the rhodium systems, catalyst life was also enhanced and yields of up to 280 mol/mol Rh with > 98% selectivity to linear dialkyl hexenedioates have been observed. Optimal conditions involved the use of [(C2H4)2RhCl]2, FeCl3 and methanol in the proportions 1:5:10 at 80 °C. The isomeric composition of the product is markedly influenced by the combination of catalyst and promoter employed; either cis-Δ2, trans-Δ2, or trans-Δ3 hexenedioate may predominate. Thus on changing the promoter from FeCl3 to SnCl4 in the Rh-catalyzed system, the product distribution changed from 85% trans-Δ2 to 62% cis-Δ2 hexene-dionate; certain Pd-catalyzed systems produced up to 60% of the isomeric Δ3 hexenedioates. © 1985.
Nugent, W. A., & McKinney, R. J. (1985). Linear dimerization of acrylates by palladium and rhodium catalysts: effect of lewis and protic acid additives. Journal of Molecular Catalysis, 29(1), 65–76. https://doi.org/10.1109/INMIC.2012.6511508