Phosphino Carboxylic Acid Ester Functionalized Carbosilane Dendrimers:  Nanoscale Ligands for the Pd-Catalyzed Hydrovinylation Reaction in a Membrane Reactor

Abstract

Phosphino carboxylic acid ester terminated G 0 compounds Si{(CH 2 ) 3 SiMe 2 (C 6 H 4 CH 2 OC(O)(CH 2 ) n -CH 2 PPh 2 } 4 (9a and 9b; n ) 1, 2) and the carbosilane dendrimers Si{(CH 2 ) 3 Si((CH 2 ) 3 SiMe 2 (C 6 H 4 -CH 2 OC(O)(CH 2 ) n CH 2 PPh 2 ) 3 } 4 (10a and 10b; n ) 1, 2) have been prepared as hemilabile nanoscale ligands for the palladium-catalyzed codimerization of olefins. The hydrovinylation of styrene was carried out in a continuously operated nanofiltration membrane reactor. Under continuous conditions, the selectivity of the reaction is increased considerably. Monomeric model complexes and the dendritic catalysts were compared for their activity and selectivity in batch reactions. The Pd catalyst complexes were prepared in situ from the dendritic ligands and an (allyl)palladium(II) precursor.

Palladium and Platinum Units Grafted on the Periphery of Carbosilane Dendrimers

“…[25] However, polynuclear complexes 1d and 3d are more active compared with other dendritic catalysts containing 8 and 12 terminal bidentate PO coordinating atoms on the surface. [24] Moreover, the good selectivity of our dendrimers towards 3-phenyl-1-butene is remarkable.…”

“…The same effect was observed by Vogt and van Koten in similar hemilabile PO-stabilized dendritic precursors. [24] Probably, the dendrimers block some of the space that olefins can use in their approach to the palladium atoms, the active sites. However, it is remarkable that the activity of the biggest system 3d is higher or similar to that of 1d (Entries 5 and 6) in spite of the fact that the first shows 8 PPh 2 groups in comparison with the 4 PPh 2 ligands displayed by the second.…”

Palladium Complexes of Phosphane-Functionalised Carbosilane Dendrimers as Catalysts in a Continuous-Flow Membrane Reactor

“…[51] They reported precipitation of palladium metal in the reactor and on the surface of the membrane. The deactivation was attributed to the formation of multiply coordinated phosphane complexes and multinuclear phosphane-bridged complexes, possibly as a result of the high local concentration of phosphane at the periphery of the dendrimer.…”

Dendritic macromolecules containing several types of functional groups

“…Because of their controllable and well known structures, dendrimers are one of the best candidates to make nanodevices 18–26. Nanocarriers,26 nanoreactors,27–30 nanoextractions,31 nanomembranes,32 nanocomposites,33 and nanoparticles34 are only few examples of nano‐objects constructed based on dendrimers. Dendritic macromolecules containing active sites on their surface or core could be used as multidisciplinary materials in the atomic or molecular level,35–37 and actually high functionality and cavity of dendrimers is the most important reason to be novel tools for constructing nanodevices 19, 38–41…”