Synthesis of dendrimers terminated by bis(diphenylphosphinomethyl)amino ligands and use of their palladium complexes for catalyzing C-C cross-coupling reactions

The synthesis of two new series of phosphorus-containing dendrimers capped by bis(diphenylphosphinomethyl)amino groups linked to either tyramine or L-tyrosine methyl ester is reported up to the third generation (48 end groups). The corresponding complexes obtained in situ by reaction with Pd(OAc)(2) are used as catalysts in three types of C-C cross-coupling reactions, namely, Suzuki, Sonogashira, and Heck reactions, in the presence of water. A slightly positive dendritic effect is observed in the case of the Sonogashira reaction: the conversion increases when the generation (size and number of end groups) of the dendritic catalyst increases. In all cases, the series built from tyramine is more efficient than the series built from L-tyrosine, showing the influence of the local hindrance, and the dendrimers are generally more efficient than the corresponding monomers.