Pillar5arenes as Supramolecular Hosts in Aqueous Biphasic Rhodium-Catalyzed Hydroformylation of Long Alkyl-chain Alkenes

Aqueous biphasic catalysis continues to attract strong interest, especially when very hydrophobic substrates are concerned. Indeed, their insolubility in water strongly limit their transformation by water-soluble organometallic catalysts. To improve contacts between the substrate-containing organic phase and the catalyst-containing phase, one of the best solutions consists in using interfacial additives capable of supramolecularly recognize the substrate and/or the catalyst. In the present study, modified pillar5arenes are considered as interfacial additives and their performance is assessed in Rh-catalyzed hydroformylation of long alkyl-chain alkenes (higher olefins). Pillar5arenes substituted by carboxylate functions and methyl groups P5 A-(Me)(10-x)-(CH2COOMe)(x) are compared to pillar5arenes substituted by polyethylene glycol (PEG) chains (P5 A-(Me)(5)-(PEG)(5) and P5 A-(PEG)(10)). Utilization of P5 A-(Me)(10-x)-(CH2COOMe)(x) leads to high conversion and regioselectivity (linear/branched aldehyde ratio) in Rh-catalyzed hydroformylation of 1-decene and 1-hexadecene. Compared with other interfacial additives such as modified cyclodextrins, the studied pillar5arenes show lower chemo-selectivity, similar catalytic activity and higher regioselectivity.