Addition of secondary amines to activated alkenes promoted by Pd(II) complexes: Use of ammonium salts as cocatalysts

The complexes [Pd(acac)2] 1, [Pd(hfa)2] 2 (hfa = hexafluoroacetylacetonate), [Pd(CF3CO2)2] 3 and [Pd3(CH3CO2)6] 4 exhibit very different catalytic efficiency in the reaction between secondary amines and activated alkenes. Complexes 1 and 4 generally show an enhanced activity when catalytic amounts of NH4X salts (X− = low-coordinating anion) are added to the reaction mixtures. On the contrary, the activity of the perfluorurate analogues 2 and 3, which is much higher than that of 1 and 4, is generally scarcely affected by the presence of the NH4X additive. The cocatalytic effect of NH4X is comparable with that of strong acids such as CF3SO3H. The ammonium salts alone can behave as a catalyst giving an almost quantitative yield of the hydroamination product.

Five Pd(II) neutral complexes have been tested as catalysts in the addition reaction of secondary amines to activated alkenes. Those bearing perfluorurated ligands exhibit very high catalytic efficiency. A good catalytic activity is also shown by the less active species if a NH4X type cocatalyst is used. In this context, the ammonium salts behave analogously to strong acids.Figure optionsDownload as PowerPoint slide