The application of C1‐symmetrical diphosphite ligands containing furanose backbone in the Rh‐catalysed asymmetric hydroformylation of norbornene is described. The catalysts were highly active and produced exclusively exo‐norbornanecarboxaldehyde with enantioselectivities (ee) up to 71 %. Considering these promising results, the ligands were modified with a pyrene moiety to accomplish their immobilisation onto carbon materials. The corresponding Rh complexes bearing the novel pyrene‐tagged ligands were synthesised and immobilised onto multiwalled carbon nanotubes (MWCNT), reduced graphene oxide (rGO) and carbon beads (CBs). The novel catalytic systems were tested in the asymmetric hydroformylation of norbornene providing similar performance in terms of both activity and selectivity compared to the non‐immobilised systems. The recyclability of the new heterogenised catalysts was studied in the target reaction in batch mode. Nevertheless, the recycling was unsuccessful due to catalyst leaching. When used under continuous flow mode, these catalysts revealed robust and provided even higher ee than the corresponding homogeneous systems.
The
successful rhodium-catalyzed asymmetric hydroformylation and
hydroaminomethylation of α-substituted acrylamides is described
using 1,3-phosphite-phosphoramidite ligands based on a sugar backbone.
A broad scope of chiral aldehydes and amines were afforded in high
yields and excellent enantioselectivities (up to 99%). Furthermore,
the synthetic potential of this method is demonstrated by the single-step
synthesis of the brain imaging molecule RWAY.
The synthesis of β 2,2 -amino esters was successfully achieved via Rh-catalysed regioselective hydroaminomethylation of methyl methacrylate with secondary amines using the neutral precursor [Rh(acac)(CO) 2 ]. In this process, the presence of molecular sieves revealed crucial in order to access the final amino ester. For the synthesis of products containing aniline derivatives, the use of the cationic precursor [Rh(COD) 2 ]BF 4 and Me CgPPh phosphine as ligand was necessary in a mixture of toluene/ DCE as solvent. Effects of the steric and electronic properties of the amines were observed during this study. Interestingly, poisoning effect of CO in the hydrogenation of the imine intermediate was observed when benzyl amine was used.
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