A further breakthrough in biphasic, rhodium-catalyzed hydroformylation: the use of Per(2,6-di-O-methyl)-β-cyclodextrin as inverse phase transfer catalyst

N,N-Diethyl-3-toluamide Formulation Based on Ethanol Containing 0.1% 2-Hydroxypropyl-β-cyclodextrin Attenuates the Drug's Skin Penetration and Prolongs the Repellent Effect without Stickiness

N,N-diethyl-3-toluamide (DEET) is one of the most widely used insect repellents in the world. It was reported that a solution containing 6-30% cyclodextrin (CD) as a solvent instead of ethanol (EtOH) provided an enhancement of the repellent action time duration of the DEET formulation, although the high-dose CD caused stickiness. In order to overcome this shortcoming, we attempted to prepare a 10% DEET formulation using EtOH containing low-dose CDs (β-CD, 2-hydroxypropyl-β-CD (HPβCD), methyl-β-CD, and sulfobutylether-β-CD) as solvents (DEET/EtOH/CD formulations). We determined the CD concentration to be 0.1% in the DEET/EtOH/CD formulations, since the stickiness of 0.1% CDs was not felt (approximately 8 × 10^-3 N). The DEET residue on the skin superficial layers was prolonged, and the drug penetration into the skin tissue was decreased by the addition of 0.1% CD. In particular, the retention time and attenuated penetration of DEET on the rat skin treated with the DEET/EtOH/HPβCD formulation was significantly higher in comparison with that of the DEET/EtOH formulation without CD. Moreover, the repellent effect of DEET was more sustained by the addition of 0.1% HPβCD in the study using Aedes albopictus. In conclusion, we found that the DEET/EtOH/HPβCD formulations reduced the skin penetration of DEET and prolonged the repellent action without stickiness.

Rhodium-Catalyzed Aqueous Biphasic Olefin Hydroformylation Promoted by Amphiphilic Cyclodextrins

Hydroformylation is an industrial process that allows for the production of aldehydes from alkenes using transition metals. The reaction can be carried out in water, and the catalyst may be recycled at the end of the reaction. The industrial application of rhodium-catalyzed aqueous hydroformylation has been demonstrated for smaller olefins (propene and butene). Unfortunately, larger olefins are weakly soluble in water, which results in very low catalytic activity. In an attempt to counteract this, we investigated the use of amphiphilic oleic succinyl-cyclodextrins (OS-CDs) synthesized from oleic acid derivatives and maleic anhydride. OS-CDs were found to increase the catalytic activity of rhodium during the hydroformylation of water-insoluble olefins, such as 1-decene and 1-hexadecene, by promoting mass transfer. Recyclability of the catalytic system was also evaluated in the presence of these cyclodextrins.

Supramolecular Approaches To Control Activity and Selectivity in Hydroformylation Catalysis

The hydroformylation reaction is one of the most intensively explored reactions in the field of homogeneous transition metal catalysis, and many industrial applications are known. However, this atom economical reaction has not been used to its full potential, as many selectivity issues have not been solved. Traditionally, the selectivity is controlled by the ligand that is coordinated to the active metal center. Recently, supramolecular strategies have been demonstrated to provide powerful complementary tools to control activity and selectivity in hydroformylation reactions. In this review, we will highlight these supramolecular strategies. We have organized this paper in sections in which we describe the use of supramolecular bidentate ligands, substrate preorganization by interactions between the substrate and functional groups of the ligands, and hydroformylation catalysis in molecular cages.

Hydroformylation in aqueous biphasic media assisted by molecular receptors

The role of molecular receptors in aqueous biphasic hydroformylation of higher olefins is highlighted through a detailed analysis of their molecular recognition properties. The behavior of cyclodextrins and calixarenes as molecular receptors is especially emphasized and discussed. Their supramolecular interactions with the substrates and the water-soluble ligands proved to be an essential parameter guiding the reaction performances. The hydroformylation activity and chemo- and regio-selectivities can thus be accurately controlled by a suitable match between the receptor and the reaction components. Development outlooks are also presented.

Biphasic aqueous organometallic catalysis promoted by cyclodextrins: Can surface tension measurements explain the efficiency of chemically modified cyclodextrins?

Methylated and hydroxypropylated cyclodextrins (CDs) are highly efficient mass transfer promoters in biphasic aqueous organometallic processes. The surface tension measurements demonstrated that these CDs adsorb at air-water interface and allowed to determine surface excess of CD by using Gibbs adsorption equation. Interestingly, a good correlation between surface excess and catalytic activity was obtained in the case of hydroformylation and Tsuji-Trost reactions. These results point out the importance of CD adsorption at the interface in biphasic aqueous organometallic processes.

Adsorption at the Liquid−Liquid Interface in the Biphasic Rhodium Catalyzed Hydroformylation of Olefins Promoted by Cyclodextrins: A Molecular Dynamics Study

Using molecular dynamics (MD) simulations, we investigate the interfacial distribution of partners involved in the phase transfer rhodium catalyzed hydroformylation of olefins promoted by beta-cyclodextrins (beta-CDs). The beta-CDs, the reactant (alkene), product (aldehyde), several rhodium complexes (the catalyst, its precursor, and its alkene adduct) are simulated at the water-"oil" interface, where oil is represented by chloroform or hexane. It is shown that unsubstituted beta-CD and its 6-methylated and 2,6-dimethylated analogues adsorb at the interface, whereas the liposoluble permethylated CD does not. The precursor of the catalyst [RhH(CO)(TPPTS)3]9- (with triphenylphosphine trisulfonated TPPTS3- ligands) sits in water, but the less charged [RhH(CO)(TPPTS)2]6- catalyst and the [RhH(CO)(TPPTS)2(alkene)]6- reaction intermediate are clearly surface active. The TPPTS3- anions also concentrate at the interface, where they adopt an amphiphilic conformation, forming an electrical double layer with their Na+ counterions. Thus, the most important key partners involved in the hydroformylation reaction concentrate at the interface, thereby facilitating the reaction, a process which may be further facilitated upon complexation by CDs. These results point to the importance of adsorption at the liquid-liquid interface in the two-phase hydroformylation reaction of olefins promoted by beta-CDs and provide microscopic pictures of this peculiar region of the solution.

Rhodium Complexes Non-Covalently Bound to Cyclodextrins: Novel Water-Soluble Supramolecular Catalysts for the Biphasic Hydroformylation of Higher Olefins

A new class of cationic alpha-cyclodextrins bearing 2-hydroxy-3-trimethylammoniopropyl groups has been synthesised. We investigated their efficiency as mass-transfer promoters in a biphasic hydroformylation reaction catalysed by a rhodium trisulfonated triphenylphosphine system. These cationic alpha-cyclodextrins greatly increased the reaction rate, the chemoselectivity, and, surprisingly, the linear-to-branched aldehyde ratio. We attributed this unexpected enhancement of the linear-to-branched aldehyde ratio to the in situ formation of new catalytic supramolecular species obtained by ion-exchange between the catalyst ligand and the cationic alpha-cyclodextrins.