The efficient reversible functionalization of the periphery of urea adamantyl poly(propylene imine) dendrimers with catalytic sites using noncovalent interactions is described. Phosphine ligands equipped with urea acetic groups, a binding motive complementary to that of the dendrimer host, have been prepared and assembled to the dendrimer support. The resulting supramolecular complex has been used as a multidentate ligand system in the palladium-catalyzed allylic amination reaction in a batch process and in a continuous-flow membrane reactor. We found that the activity and selectivity of the dendrimeric complex is similar to that of the monomer complex, which indicates that the catalytic centers act as independent sites. The size of the supramolecular system is sufficiently large and the binding of the guests is strong enabling a good separation of the catalyst components from the reaction mixture using nanofiltration techniques.

Phosphine functionalised carbosilane dendrimers have been synthesised and their palladium complexes used as catalysts in the allylic alkylation reaction performed in a continuous flow membrane reactor.

Phosphane‐functionalised carbosilane dendrimers 9, 10, 11, 12, 13, 19 and 20 have been synthesised, and their palladium complexes have been used as catalysts in the allylic substitution reaction. The catalytic sites at the periphery of the dendrimer support are readily accessible to the substrate, which is reflected − also for the larger dendrimeric systems − in the high catalytic activity. Moreover, the higher generations are sufficiently large to be retained by a nanofilter, and dendrimeric catalysts 13 and 20 have been applied in a continuous‐flow membrane reactor. The stability of the palladium complexes of the phosphane‐functionalised dendrimers is crucial for application in a continuous process of this type, and appeared to be very sensitive to small changes in the dendrimeric structure. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Quantitative aspects of submicroscopic autoradiography, using the flat substrate technique, were studied. Using Kodak D19b as developer efficiency values of about 37 for the Ilford LA emulsion and about 17 for the Gevaert-Agfa Scientia Nuc 3.07 emulsion were obtained with H3-methacrylate sections of gray interference colors. Theoretical and experimental data revealed that the high standard deviations of efficiency values obtained are caused mainly by variations in section thickness within ribbons of sections, which on account of identical interference colors were considered to be equally thick. Measurements of efficiency on sections with thickness variations between 400 and 2500 Å revealed that self-absorption is an important factor in tritium autoradiography at the electron microscopic level.