Efficacies of multivalent vs monovalent poly(ether imine) dendritic catalysts within a generation in multiple C–C bond forming reactions

Dendrimers are ideal platforms to study multivalent effects due to the presence of uniform end groups at their peripheries. This report concerns with a study of multivalent dendritic catalysts, both within and across dendrimer generations, and their effects to mediate C–C bond forming reactions on multivalent substrates that have two and three acrylate reactive sites. As many as fourteen multivalent dendritic catalysts were prepared using 0–3 generations of poly(propyl ether imine) dendrimers, incorporated with Pd(II) catalytic sites, both within and across the dendrimer generations. C–C Bond forming reactions of these substrates with iodobenzene, mediated by uniform concentration of the metal across all catalysts, showed formation of partially and fully functionalized cinnamates in varying ratios, depending on the extent of clustering of catalytic moieties at the peripheries of dendrimers within a dendrimer generation. In a given generation, higher clustering of catalytic moieties greatly assisted multiple C–C bond formations than presenting the same in lesser number. The studies demonstrate true benefits of clustering catalytic moieties within a dendrimer generation and the beneficial effects applicable to catalysis of substrates presenting more than one reactive center.

Multivalent dendritic catalysts of poly(propyl ether imine) dendrimer of 0–3 three generations were utilized in the Heck coupling reactions of multivalent substrates possessing two and three reactive sites. Significant increases in the formation of multi-Heck coupling products were observed for the fully or mostly functionalized dendritic catalysts when compared to dendrimers incorporated with lesser number of catalytic moieties. The observations establish multivalent effects in catalysis, realized through dendritic catalysts arising from both within and across generations.Figure optionsDownload as PowerPoint slideHighlights
► A study of the efficiencies of monovalent and multivalent dendritic catalysts.
► Fourteen multivalent catalysts prepared from 0 to 3 generations of PETIM dendrimers.
► Multiple C–C bond formations on substrates catalyzed by multivalent catalysts.
► Multivalent catalysts are superior to mediate multiple C–C bond formation reactions.
► 31P NMR studies to identify intermediates in the mono- and multivalent catalysts.