Immobilisation of the BINAP Ligand on Dendrimers and Hyperbranched Polymers: Dependence of the Catalytic Properties on the Linker Unit

Abstract

A series of immobilised Carbo-BINAP ligands has been synthesised using poly(propylene imine) (PPI) dendrimers as soluble supports. They contain up to 64 BINAP ligands at their periphery without an additional linking unit. Despite the high steric requirements of the ligand, all dendrimers could be completely functionalised, resulting in the immobilised systems in good yields. Furthermore, the immobilisation strategy that worked out for the fixation of AMINAP ligands with additional linking units as well as of Carbo-BINAP ligands without additional linking units on dendrimers has thus been extended to less regularly hyperbranched poly(ethylene imines) (PEI) as soluble supports. In that way it has been possible to attach on average 9, 26, and 138 Glutaroyl-AMINAP or Carbo-BINAP ligands to PEIs of different molecular weights. The catalytic properties of these systems in the copper-catalysed hydrosilylation of acetophenone were investigated. The dendritic PPI-bound Carbo-BINAP ligands displayed a strong dependence of enantioselectivity and activity on the generation of the dendrimer. For the Carbo-BINAP and Glutaroyl-AMINAP ligands immobilised on the hyperbranched polymers, however, activities and enantioselectivities comparable to those of the mononuclear catalysts were found. The macromolecular, immobilised BINAP ligands could be recycled several times without any observable loss of activity or enantioselectivity.

Recent progress in homogeneous supported asymmetric catalysis: example of the BINAP and the BOX ligands

“…Only a few other applications of the supported BIN-AP ligands were described, such as a Rh-hydroboration reaction of vinylarenes 13 and Cu-hydrosilylation of acetophenone. 14,15 While the Wilkinson's Ru II -BINAP complex was very effective in the hydrogenation of olefins, the same catalyst was not very active for the hydrogenations of ketones. Noyori had shown that the association with a stoichiometric amount of 1,2-diphenylethylenediamine (DPEN) accelerates the hydrogenation of ketones by a metal-ligand bifunctional catalysis mechanism.…”

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

“…Supplementary data related to this article can be found online at doi: 10.1016/j.jorganchem.2011. 11.026.…”

“…Studies by number of groups further established the effectiveness of dendritic catalysts. Astruc [9] and co-workers, and Gade [10] and co-workers demonstrated a negative dendritic effect in CeC bond forming reactions and hydrogenation reactions, respectively. On the other hand, Majoral and co-workers [11] showed a positive dendritic effect with phosphorous containing dendrimer in selected organometallic reactions.…”

Reduction of Sulfoxides to Sulfides in the Presence of Copper Catalysts

“…Besides molybdenum-, iron-, and zinc-based systems the application of copper can be beneficial. Indeed, the potential of copper catalyst in reduction techniques has been explored in the reduction of various functionalities [46][47][48][49][50][51][52][53][54][55][56][57][58]. However, the catalytic reduction of sulfoxides in the presence of copper has been so far unreported, while the converse process has been studied [59].…”