Giorgio La Sorella

Recent advances in catalysis in micellar media

The present review paper deals with the development of catalytic systems in water in the presence of micelles obtained by addition of surfactants, focusing on the effects of these simple, economic, and green reaction media on important aspects like recyclability, activity, product and substrate selectivity. Contributions from 2005 to 2014 are surveyed with particular emphasis on emerging findings and directions in the field of catalysis. Surfactants enable formation of nanosized apolar aggregates in bulk water where the catalysts and reagents can be dissolved thanks to weak intermolecular interactions like the hydrophobic effect and ion pairing operating in a more concentrated system compared to the bulk solvent. While in the past the use of surfactants was a straightforward approach to enable solubilization of reaction mixtures in water, nowadays specific interactions between substrates, catalysts and micelles are investigated by means of NMR and other techniques to better understand the molecular basis of this kind of supramolecular catalysis. Specifically designed surfactants to engineer micelles in order to compete efficiently with traditional catalysis in organic solvents are nowadays available.

Efficient isonitrile hydration through encapsulation within a hexameric self-assembled capsule and selective inhibition by a photo-controllable competitive guest

Catalytic hydration of neutral isonitriles to yield the corresponding N-formylamides was achieved by reversible encapsulation in a self-assembled hexameric resorcin[4]arene capsule. Encapsulation of a photochromic dithienylethene bis-cation provides different levels of competitive inhibition depending on the geometry assumed by the cationic inhibitor.

Micellar Promoted Multi-Component Synthesis of 1,2,3-Triazoles in Water at Room Temperature

Micellar media in water provide a simple and efficient environment favoring the multi-component synthesis of 1,2,3-triazoles from organic bromides, sodium azide and terminal alkynes in the presence of [Cu(IMes)Cl] 1 catalyst at room temperature within a few hours. The micellar medium favors both the in situ formation of the organic azide and its metal promoted cycloaddition with the alkyne.

Supramolecular Encapsulation of Neutral Diazoacetate Esters and Catalyzed 1,3-Dipolar Cycloaddition Reaction by a Self-Assembled Hexameric Capsule

Diazoacetate esters proved to be suitable neutral guests for the self‐assembled resorcin[4]arene hexameric capsule. The hydrogen‐bonded supramolecular host catalyzed the 1,3‐dipolar cycloaddition reaction between diazoacetate esters and electron‐poor alkenes such as acrolein, acrylonitrile, predominantly trans‐crotonaldehyde, trans‐2‐hexenal, methyl, and butyl acrylate, which led to the corresponding 4,5‐dihydro‐1H‐pyrazole derivatives. The cycloaddition reaction occurred within the cavity of the capsule. In fact, substantial inhibition of the catalytic activity was observed by employing tetraethylammonium tetrafluoroborate characterized by greater affinity for the hexameric capsule as a competitive guest; its presence inhibited access of the substrates. The 1,3‐dipolar cycloaddition reaction between diazoacetate esters and acrylate esters of different lengths showed a significant degree of substrate selectivity owing to the encapsulation of the reagents before the cycloaddition reaction.

Hydration of aromatic alkynes catalyzed by a self-assembled hexameric organic capsule

The combination of a Bronsted acid catalyst and a supramolecular organic capsule formed by the self-assembly of six resorcin[4]arene units efficiently promotes the mild hydration of aromatic alkynes to their corresponding ketones. The capsule provides a suitable nanoenvironment that favors protonation of the substrate and addition of water.

Surfactant-Induced Substrate Selectivity in the Palladium-Nanoparticle-Mediated Chemoselective Hydrogenation of Unsaturated Aldehydes in Water

A hundred‐fold substrate selectivity was observed in the competitive chemoselective hydrogenation of seven α,β‐unsaturated aldehydes from C4 to C10 in water with palladium nanoparticles stabilized by sodium dodecyl sulfonate as the surfactant. The medium makes the longer lipophilic substrates hundreds of times more reactive than the shorter more hydrophilic ones, whereas in an organic medium almost no difference is observed.

Aqueous biphasic treatment of some nitrocompounds with hydrogen in the presence of a biogenerated Pd-polysaccharide

A strain of Klebsiella oxytoca BAS-10, known to produce a specific exopolysaccharide (EPS), when grown aerobically in static mode in the presence of Pd(NO3)2, generated the species Pd-EPS that was used as catalyst precursor in the aqueous biphasic treatment of some nitrocompounds with hydrogen. Nitrobenzene was hydrogenated to aniline with almost quantitative yields and the catalyst, embedded in the aqueous phase, was used with success and with near the same efficiency in three recycling experiments. In the case of 1-iodo-4-nitrobenzene only nitrobenzene was obtained while the unsaturated nitro compound β-methyl-β-nitrostyrene afforded both the corresponding oxime and the saturated nitro derivative.

Selective Hydrogenations and Dechlorinations in Water Mediated by Anionic Surfactant Stabilized Pd Nanoparticles

We report a facile, inexpensive, and green method for the preparation of Pd nanoparticles in aqueous medium stabilized by anionic sulfonated surfactants sodium 1-dodecanesulfonate 1a, sodium dodecylbenzenesulfonate 1b, dioctyl sulfosuccinate sodium salt 1c, and poly(ethylene glycol) 4-nonylphenyl-3-sulfopropyl ether potassium salt 1d simply obtained by stirring aqueous solutions of Pd(OAc)2 with the commercial anionic surfactants further treated under hydrogen atmosphere for variable amounts of time. The aqueous Pd nanoparticle solutions were tested in the selective hydrogenation reactions of aryl-alcohols, -aldehydes, and -ketones, leading to complete conversion to the deoxygenated products even in the absence of strong Brønsted acids in the reduction of aromatic aldehydes and ketones, in the controlled semihydrogenation of alkynes leading to alkenes, and in the efficient hydrodechlorination of aromatic substrates. In all cases, the micellar media were crucial for stabilizing the metal nanoparticles, dissolving substrates, steering product selectivity, and enabling recycling. What is interesting is also that a benchmark catalyst like Pd/C can often be surpassed in activity and/or selectivity in the reactions tested by simply switching to the appropriate commercially available surfactant, thereby providing an easy to use, flexible, and practical catalytic system capable of efficiently addressing a variety of synthetically significant hydrogenation reactions.