Sandra Niembro

Perfluoro-tagged, phosphine-free palladium nanoparticles supported on silica gel: application to alkynylation of aryl halides, Suzuki–Miyaura cross-coupling, and Heck reactions under aerobic conditions

The utilization of perfluoro-tagged palladium nanoparticles immobilized on fluorous silica gel through fluorous–fluorous interactions (Pdnp–A/FSG) or through covalent bonding to silica gel (Pdnp–B) in the alkynylation of aryl halides, in the Suzuki–Miyaura cross-coupling, as well as in the Heck reaction between methyl acrylate and aryl iodides is described. The reactions are carried out under aerobic and phosphine-free conditions with excellent to quantitative product yields in each case. The catalysts are easily recovered and reused several times without significant loss of activity. The alkynylation of aryl halides (under copper-free conditions) and the Suzuki–Miyaura cross-coupling are carried out in water. The Heck reaction of methyl acrylate with aryl iodides is best performed in MeCN. The utilization of Pdnp–B in the synthesis of 2,3-disubstituted indoles from 2-(alkynyl)trifluoroacetanilides and aryl halides is also reported.

Palladium nanoparticles supported on an organic-inorganic fluorinated hybrid material. Application to microwave-based heck reaction.

Phosphine-free palladium nanoparticles were embedded in a fluorous organic-inorganic hybrid material 6b prepared by the sol-gel process. The use of Pdn.6b in the Heck coupling reaction under microwave irradiation has been investigated. Recycling studies have shown that the catalyst can be readily recovered and reused several times without significant loss of activity. Reactions and recovery of the solid-supported palladium catalyst system can be carried out in the presence of air, without any particular precaution.

Phosphine-Free Perfluoro-Tagged Palladium Nanoparticles Supported on Fluorous Silica Gel: Application to the Heck Reaction†

The immobilization of phosphine-free perfluoro-tagged palladium nanoparticles Pd-1 on fluorous silica gel (FSG) and their utilization in the Heck reaction have been investigated. High yields of vinylic substitution products have been obtained. Recycling studies have shown that the solid-supported palladium catalyst can be readily recovered and reused several times without significant loss of activity. Reactions and recovery of the solid-supported palladium catalyst system can be carried out in the presence of air, without any particular precaution.

The Heck Reaction of Allylic Alcohols Catalyzed by Palladium Nanoparticles in Water: Chemoenzymatic Synthesis of (R)‐(−)‐Rhododendrol

The use of phosphine‐free perfluoro‐tagged palladium nanoparticles immobilized on fluorous silica gel (FSG), either through fluorous–fluorous interactions or covalent bonding, in the Heck reaction of aryl iodides with allylic alcohols under aerobic conditions in water is described. 4‐(4‐Methoxyphenyl)‐butan‐2‐one, an important fine chemical, is readily accessed by this procedure. A two‐step one‐pot process, involving a Heck reaction followed by an enantioselective enzyme‐catalyzed reduction, to form chiral alcohols is applied to the synthesis of (R)‐(−)‐rhododendrol. The palladium catalysts can be recycled several times, both in the Heck reaction and in the one‐pot chemoenzymatic process.

Alkynylation of aryl halides with perfluoro-tagged palladium nanoparticles immobilized on silica gel under aerobic, copper- and phosphine-free conditions in water

The utilization of perfluoro-tagged palladium nanoparticles immobilized on fluorous silica gel through fluorous-fluorous interactions (Pd(np)-/FSG) or linked to silica gel by covalent bonds (Pd(np)-) in the alkynylation of terminal alkynes with aryl halides under aerobic, copper- and phosphine-free conditions in water, and their recovery and re-utilization, is described.

Star-shaped heavily fluorinated aromatic sulfurs: stabilization of palladium nanoparticles active as catalysts in cross-coupling reactions

Two star-shaped heavily fluorinated compounds have been prepared and used as stabilizers of palladium nanoparticles. These materials are useful and reutilizable catalysts in Mizoroki–Heck, Suzuki and Sonogashira cross-couplings.

Perfluoro-tagged rhodium and ruthenium nanoparticles immobilized on silica gel as highly active catalysts for hydrogenation of arenes under mild conditions

Perfluoro-tagged rhodium and ruthenium nanoparticles have been stabilized on highly fluorinated hybrid organic–inorganic silica gel. The method for preparation of these nanoparticles is highly reproducible and the new materials were robust, recoverable and active catalysts for arene hydrogenation under very mild conditions.

Perfluoro-Tagged Gold Nanoparticles Immobilized on Fluorous Silica Gel: A Reusable Catalyst for the Benign Oxidation and Oxidative Esterification of Alcohols

We recently showed that palladium nanoparticles stabilized by perfluoro-tagged phosphine-free compounds and immobilized on fluorous silica gel (FSG) by fluorous–fluorous interactions can be used in C C bond forming reactions, such as the Heck reaction and the alkynylation of aryl iodides. The ease with which precatalysts of this type can be prepared, combined with their efficiency and recyclability, makes these materials an attractive simple alternative to the large number of heterogeneous palladium precatalysts reported to date. Therefore, as part of a program devoted to the investigation of the scope of this immobilization methodology and to its extension to other transition metals, we were led to investigate the immobilization of gold nanoparticles stabilized by heavily fluorinated compounds on fluorous silica gel and their utilization in the oxidation of alcohols. The development of efficient catalytic systems for the oxidation of alcohols is a subject of great importance both from an economic and environmental point of view. Recently, considerable attention has been dedicated to catalytic processes based on the use of molecular oxygen as a terminal oxidant, with water as the harmless byproduct. 5] This approach provides significant advantages over the classical methods based on metal oxides that lead to the generation of problematic metal waste. In this context, the utilization of gold nanoparticles as catalysts has attained a prominent role. Herein we describe the use of recyclable and easily made gold nanoparticles, stabilized by perfluoro-tagged compounds and immobilized on fluorous silica gel, in the oxidation of alcohols. Perfluoro-tagged gold nanoparticles Aunp–A (diameter 2.7 0.6 nm; 17.3 % w/w gold) were prepared as described previously for similar systems, by reduction of HAuCl4 with NaBH4 in EtOH at room temperature in the presence of stabilizing thiol A bearing two perfluorinated chains (Scheme 1 and Figure 1 a). Compound A was prepared through stepwise functionalization of the less expensive cyanuric chloride. Selective substitution of two chlorides was achieved in a quantitative yield using two equivalents of 1H,1H,2H,2H-perfluorodecanethiol in THF at 0 8C, and diisopropylethylamine (DIPEA) as a base. The remaining chloride was substituted by sodium sulfide, giving A in 79 % yield. The electron diffraction patterns of Aunp–A (Figure 1 b) show diffraction rings that were ascribed to the (111), (200), (220), and (311) crystallographic planes of the face-centered cubic (fcc) Au. Using this method, two immobilized precatalysts were prepared as air-stable powders: Aunp–A/FSG-1, containing 6.6 mg of Aunp per gram of FSG, and Aunp–A/FSG-2, containing 3.3 mg of Aunp per gram of FSG. Transmission electron microscopy (TEM) of these precatalysts was carried out. The mean diameter of the nanoparticles in Aunp–A/FSG-1 was about 1.9 0.3 nm Scheme 1. Synthesis of the gold nanoparticles Aunp–A/FSG and the stabilizer A.

Gold nanoparticles decorated with a cinchonine organocatalyst: application in the asymmetric α-amination of β-ketoesters

A straightforward method for loading a thiol cinchonine derivative onto the surface of gold nanoparticles is described. The material was found to be an effective heterogeneous catalyst in the asymmetric α-amination of β-ketoesters.