Valerica Pandarus

The Sol–Gel Route to Advanced Silica-Based Materials and Recent Applications

Applications Rosaria Ciriminna,† Alexandra Fidalgo,‡ Valerica Pandarus, Franco̧is Beĺand, Laura M. Ilharco,*,‡ and Mario Pagliaro*,† †Istituto per lo Studio dei Materiali Nanostrutturati, CNR, via U. La Malfa 153, 90146 Palermo, Italy ‡Centro de Química-Física Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tećnico, Complexo I, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal SiliCycle Inc., 2500, Parc-Technologique Boulevard, Quebec City, Quebec G1P 4S6, Canada

Heterogeneous versus Homogeneous Palladium Catalysts for Cross-Coupling Reactions

A large number of immobilized‐Pd‐catalysts for cross‐coupling reactions have been introduced in the last decade. Are the observed catalyzed reactions truly heterogeneous or are they homogeneous due to leached palladium? This account critically addresses the leaching issue by selectively referring to some of the newly developed catalytic systems in an attempt to evaluate said systems based on uniform criteria. The report is concluded by identifying the relevant chemical and structural challenges in the field.

A new class of heterogeneous Pd catalysts for synthetic organic chemistry

A new series of leach-proof nanostructured Pd(0) catalysts able to catalyze a number of fundamental organic transformations including C–C bond formation has been developed. Reactions in general proceed with high yield and often at completion, while the catalysts can be reused in further reaction runs. This establishes a new class of relevant solid catalysts for synthetic organic chemistry trademarked SiliaCat Pd0 Hydrogel.

Selective hydrogenation of functionalized nitroarenes under mild conditions

Functionalized anilines are selectively synthesized from the corresponding nitroarenes by simple heterogeneous catalytic hydrogenation carried out under mild conditions over a very low amount (0.5 mol%) of a new sol–gel entrapped Pd(0) catalyst. Only halo-nitroarenes could not be selectively converted. The catalyst is leach-proof and can be reused in many consecutive reaction cycles.

SiliaCat Diphenylphosphine Palladium(II) Catalyzed Borylation of Aryl Halides

We investigate the heterogeneously catalyzed direct synthesis of boronic acid pinacol esters using a wide range of aryl chlorides, bromides, and iodides, and bis(pinacolato)diboron as the borylating agent over the sol–gel entrapped SiliaCat diphenylphosphine palladium(II) catalyst. Optimization of the reaction conditions, scale‐up of the optimized process, and analysis of palladium leaching enabled us to establish a new selective route for direct access to a diverse set of boronic acid pinacol esters.

Selective Debenzylation of Benzyl Protected Groups with SiliaCat Pd(0) under Mild Conditions

Protection of functional groups such as alcohols, acids, and amines in the manufacture of pharmaceuticals and fine chemicals is often necessary to avoid possible side reactions during the typical multi-step syntheses of complex organic molecules carried out by these industries. Formation of benzyl esters and ethers (O-protection) is a commonly used protection method in numerous drugs syntheses, as the Bn protecting group features ease of preparation and chemical stability toward a number of reaction conditions. Selective and smooth deprotection is critical, and the commonly used method makes use of catalytic hydrogenolysis of protecting benzylic groups with H2 under pressure in the presence of a heterogeneous Pd/C catalyst or Raney Ni. Often, however, the deprotection reaction conditions are not compatible with other functional groups, such as nitro, unsaturated bonds, and halogen groups. For example, the state of the art Pd/C catalyst for the O-debenzylation of benzyl protected alcohols and acids makes use of the following recommended reaction conditions:

New Catalyst Series from the Sol–Gel-Entrapment of Gold Nanoparticles in Organically Modified Silica Matrices: Proof of Performance in a Model Oxidation Reaction

Gold nanoparticles were sol–gel‐entrapped in the mesoporous structure of organically modified silica matrices, and the resulting SiliaCat Au materials were tested as oxidation catalysts in the model reaction of 1‐phenylethanol with hydrogen peroxide. The new materials were characterized by electronic microscopy, IR spectroscopy, and cryogenic N2 sorption. The results point to conclusions of general validity that allow us to advance towards the practical use of supported gold nanoparticles in a number of applications.

Characterization of Nanostructured SilicaCat Pd0

Structural investigation on nanostructured SiliaCat Pd0 palladium catalyst sheds light into the origins of the remarkable activity of these new catalytic materials.Graphical Abstract

Heterogeneously Catalyzed Hydrogenation of Squalene to Squalane under Mild Conditions

The full chemoselective hydrogenation of highly unsaturated all‐trans linear squalene into valuable fully saturated squalane is achieved smoothly under mild conditions over the sol–gel‐entrapped Pd catalyst SiliaCat Pd0. The catalysis is truly heterogeneous, and the catalyst is stable and recyclable, which opens the route to an easier and less expensive hydrogenation of squalene.

Clean and fast cross-coupling of aryl halides in one-pot

Summary Unsymmetrically coupled biaryls are synthesized in high yield starting from different aryl bromides and bis(pinacolato)diboron by carrying out the Miyaura borylation reaction followed by the Suzuki–Miyaura reaction in the same reaction pot over 1–2 mol % SiliaCat DPP-Pd. The SiliaCat DPP-Pd catalyst is air-stable and the method does not require the use of inert conditions. The use of non-toxic isopropanol or 2-butanol as reaction solvent further adds to the environmental benefits of this new green synthetic methodology.