Highly Efficient Rh‐catalysts Immobilised by π‐π Stacking for the Asymmetric Hydroformylation of Norbornene under Continuous Flow Conditions

Abstract

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.

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

“…In 2019, a supported catalyst for AHF was developed by Garcia-Suarez, Godard and co-workers [ 565 ]. The employed ligands consists of 1,3-diphosphites with furanose backbone carrying a pyrene functional group capable of π–π stacking interactions with hydrophobic supports.…”

Recent Advances in Continuous‐Flow Enantioselective Catalysis

“…However, the conversion only reached 15 %. To improve the recovery efficiency of the catalyst, the Godard group developed an immobilization protocol in which pyrene‐tagged 38 was immobilized onto multiwalled carbon nanotubes (MWNT), reduced graphene oxide (rGO), and carbon beads (CBs) by π–π interactions. The results show that 38 @CBs increased the conversion up to 35 % and maintained a higher enantioselectivity (72 % ee ) with lower decay in activity in the flow process than the corresponding reaction in the batch process.…”

Polymeric Heterogeneous Catalysts in the Hydroformylation of Unsaturated Compounds

“…For historical perspective, mention should be made of the scientifi c studies where different types of inorganic carriers such as silicon oxide [4][5][6][7], zeolites [8][9][10], and activated carbon [11,12] were used as materials for immobilization of metal complexes. The range of insoluble carriers used in the processes was considerably expanded thereafter, and at present the main metal fi xing methods include: incorporation of metal nanoparticles into the structures of various materials [13,18]; fi xing the rhodium complexes in the structure of the material by intercalation [19]; encapsulation of phosphine or a phosphine complex into mesopores or nanopores of the carrier [20,21]; the sol-gel method, "grafting" of a phosphine-containing hydrocarbon radical onto the carrier surface, and other methods of covalent bonding of phosphine fragments on an inorganic, hybrid or organic substrate, wherein rhodium is subsequently introduced [22][23][24][25][26][27][28]; fi xing of phosphine or a phosphine complex on the surface by means of ionic interactions [29]; fi xing of catalysts soluble in polar liquids (water and ionic liquid) in the thin hydrophilic layer of the carrier, which most frequently is silica gel SAPC/SIPC (Supported Aqueous/Ionic Liquid Phase Catalysts) [30,31]; creation of structures containing single rhodium atoms, as per the "single atom" concept [32], such as the cases in which nano-objects (nanosheets and nanofi bers) made of cobalt oxide [33] or zirconium oxide [34] were obtained and their catalytic properties were studied. Heterogeneous modifi ed rhodium clusters [35] and an iron-based catalyst [36] are also reported to have been used.…”