Abstract Cyclodextrins or calixarenes possessing extended hydrophobic host cavities and surface‐active properties were found to be very efficient as mass transfer promoters for the palladium‐mediated Suzuki cross‐coupling reaction of 1‐iodo‐4‐phenylbenzene and phenylboronic acid in aqueous medium. The cross‐coupling rates were up to 92 times higher than those obtained without addition of any compound.
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Abstract Concerns about the environmental impact of chemical transformations prompted chemists to develop clean chemical processes using water as a solvent. Although appropriate for small partially water‐soluble molecules, these processes do not allow for the transformation of hydrophobic substrates due to the mass transfer limitation between the aqueous and the organic phase. In this context, we show that activated carbons can be used as mass transfer additives to promote the rhodium‐catalyzed hydroformylation of methyl oleate and other unsaturated olefins. Due to its mesoporous and hydrophobic character, the Nuchar®WV‐B activated carbon proved to be especially effective as mass transfer promoter. Actually, a significant increase in the conversion was observed. Additionally, more than 90% aldehydes were formed during the course of the reaction. When compared to other mass transfer promoters such as co‐solvents or cyclodextrins, Nuchar®WV‐B was by far the most efficient. Thus, the use of activated carbons appeared to be a suitable solution for the aqueous rhodium‐catalyzed hydroformylation of hydrophobic bio‐sourced substrates. Practical applications: The easiness with which the FAME hydroformylation could be implemented in water using activated carbons as mass transfer promoters is a major advantage in a context of an industrial–environmental approach. This finding is of importance as the obtained oxo‐products can be used in many industrial areas such as surfactants, polymers, or lubricants.
During these last years, cyclodextrins (CDs) have greatly contributed to the development of innovative homogeneous or heterogeneous catalytic processes. More than simple molecular platforms aiming at designing new ligands or interfacial additives, CDs have been employed to generate unconventional reaction media such as supramolecular hydrogels or low melting mixtures (LMMs) capable of stabilizing active catalytic species. By using such alternative and unconventional media, high catalytic activities and selectivities were obtained in various transition metal catalytic reactions. The studied catalytic systems are easy to implement and allow for the remarkable stabilization of organometallic or metal nanoparticle catalysts. Interestingly, the size of metal nanoparticles can be finely tuned through confinement in the network of CD-based supramolecular hydrogels. Additionally, the catalysts can be recovered by a simple phase separation. The catalytic phase can be stored at room temperature under an air atmosphere in the solid state and reused as needed without significant loss of activity. Eventually, such CD-based catalytic systems greatly improve process safety. The present article intends to show the reader the very substantial progress that has recently been made in the field.
The ruthenium-catalyzed hydrogenation of water-insoluble aldehydes in an aqueous/organic two phase system has been investigated in the presence of cosolvents or cyclodextrins. At low content, i.e. a content that enables to recover quantitatively the catalytic system without loss of metal with a cosolvent, β-cyclodextrin and its dimethylated form appear to be more efficient than cosolvents for performing the reaction. The formation of inclusion complexes between cyclodextrin and various components of the reaction medium (aldehyde, alcohol, hydrocarbon of the organic phase) is discussed on the basis of mass spectrometry, NMR and catalytic experiments.
