Armelle Ouali

Dendrimers : towards catalytic, material and biomedical uses

This book will be mainly focussed on the properties and uses of dendrimers and dendrons. The aim of this book is to be the reference book about dendrimers applications. It will not describe all details, but it will give the reader a unique overview of what has currently been done with dendrimers, with numerous references and illustrations. It will be divided in four main parts: Part 1) Generalities, syntheses, characterizations and properties; Part 2) Applications in catalysis; Part 3) Applications for the elaboration or modification of materials; and Part 4) Applications in biology/medicine. The role of the nanometric size and the multiple functions of dendrimers on the properties will be emphasized.

Pyrene‐Tagged Dendritic Catalysts Noncovalently Grafted onto Magnetic Co/C Nanoparticles: An Efficient and Recyclable System for Drug Synthesis

The reuse of catalysts is highly desirable for economic and ecological reasons, and to this day constitutes an important challenge. Along these lines, magnetic nanoparticles (MNP) are increasingly recognized as appealing supports for catalytic systems in the development of more efficient and green processes. Contrary to conventional supports, such as polymers or silica, which require time-consuming precipitation and filtration steps, their separation can easily be achieved by magnetic decantation. Moreover, MNPs are mechanically robust and can be easily agitated during a reaction by application of an external magnetic field. Generally, MNPs are stabilized by coating the magnetic core with polymer or silica shells, which are used for the covalent immobilization of homogeneous catalysts. Magnetic carbon-coated nanoparticles have also been used as reusable supports for the covalent immobilization of catalysts; however, their graphene-like shell offers the unique possibility for non-covalent catalyst attachment by p–p stacking, a concept that was recently demonstrated with pyrene-tagged Pd monomeric complexes. Covalently immobilized dendronized catalysts, which possess an anchoring site and branches terminating with active sites, represent another promising strategy for recoverable catalysts, as they were shown to afford enhanced surface functionalization and better catalytic activity than corresponding monomeric catalysts. Combining both strategies, we planned to graft pyrene-tagged dendritic Pd-phosphine catalysts onto Co/C MNPs by p–p stacking, and to evaluate the activity and recyclability of the resulting composites in Suzuki reactions. Pyrene derivative 3 was prepared in high yield (91%) from commercial 1 and tyramine 2 (Scheme 1). 3 was allowed to react with N3P3Cl6 and Cs2CO3 to afford 4-G0 in 81% yield. The growth of this dendron was achieved by using the reactivity of the P Cl bonds towards phenolic group of 4-OH-

Efficient and recyclable rare earth-based catalysts for Friedel–Crafts acylations under microwave heating: dendrimers show the way

The catalytic system involving Sc(OTf)3 and a dendritic terpyridine ligand is able to promote the Friedel–Crafts acylation of a wide range of aromatics under microwave irradiation. The expected products are obtained in high yields after short reaction times and the nano-sized catalyst can be recovered and successfully used in 12 consecutive runs.

An efficient and recyclable dendritic catalyst able to dramatically decrease palladium leaching in Suzuki couplings

A series of novel monomeric and dendritic thiazolyl phosphines (generations 1 and 3) was prepared and the activity these ligands conferred to palladium in Suzuki couplings was evaluated. The heteroaryl ligands were revealed to be very efficient and were able to perform the reactions in mild conditions. Besides, their efficiency was compared to that of the corresponding triphenylphosphines. Moreover, the possibility to reuse both families of dendritic ligands was explored and the thiazolyl phosphine-based catalytic systems could be successfully recycled for five consecutive reactions without loss of activity, contrary to their triphenylphosphine counterparts. Remarkably, the palladium leaching was found to be dramatically reduced by using the dendrimer-supported thiazolylphosphines instead of the monomeric ligand and only trace amounts of metal (<0.55 ppm) could be found in the coupling product before any purification.

Well-defined poly(vinylidene fluoride) (PVDF) based-dendrimers synthesized by click chemistry: enhanced crystallinity of PVDF and increased hydrophobicity of PVDF films

This study reports the preparation by click chemistry of a novel fluorinated dendrimer bearing PVDF branches and its characterization by several analytical methods including 1H, 13C, 31P and 19F NMR, diffusional NMR, SEC, DLS, ATG, DSC and HRTEM. As remarkable properties, this dendritic PVDF displayed crystallinity (HRTEM highlighted crystalline disc-like zones of ca. 5 nm) and a much higher hydrophobicity than both its precursors with the water contact angle (WCA) reaching 108°.

Solventless synthesis of Ru(0) composites stabilized with polyphosphorhydrazone (PPH) dendrons and their use in catalysis

Ruthenium nanoparticles (NPs) are prepared by milling under air ruthenium chloride (RuCl3), sodium borohydride (NaBH4) and a polyphosphorhydrazone (PPH) dendron (generation 0 to 2) having an alkyl chain at the focal point and triarylphosphines on the surface. The resulting NPs have a diameter in the 2 to 3 nm range and they are stable upon storage in solution or as powders. They can efficiently catalyze hydrogenation of styrene. The interaction between the dendrons and the NPs is studied, and the influence of the alkyl chain length and dendron generation is also discussed.

Cyclotriphosphazene, an old compound applied to the synthesis of smart dendrimers with tailored properties

Abstract The versatile reactivity of hexachlorocyclotriphosphazene (N3P3Cl6) has been developed for the synthesis of specifically engineered dendrimers. Dendrimers are hyperbranched macromolecules built by concentric layers constituted of associated monomeric units. Many of the properties of dendrimers depend on the type of their surface (terminal) functions, which are generally all identical. For some specific purposes, it is desirable to have one function that is different at the level of the core. Hexachlorocyclotriphosphazene offers the possibility to differentiate the reactivity of one (or more) Cl from the others, for producing specifically engineered dendritic tools. These specific reactions on N3P3Cl6 have produced highly dense dendrimers, Janus dendrimers (two faces), tools for functionalizing materials, with uses as catalysts, as chemical sensors, for trapping CO2, for the culture of cells, or for imaging biological events. These properties will be emphasized in this review.

Phosphorus Dendrimers: Efficient Tools for “Greener” Catalyst Design

Abstract The use of dendrimers as soluble supports of catalytic entities offers efficient tools for “greener” catalysis. Indeed, thanks to their large size, dendrimers can be recovered and reused; depending on their structure, they can be tolerant to aqueous media or even soluble in water; and they can be used as ligands of cheap metals such as copper. We describe several examples of dendritic catalysts having such properties, based on the functionalization of phosphorus-containing dendrimers.

Catalysis Within Dendrimers

Dendrimers are hyperbranched macromolecules, synthesized step by step (generation after generation) in an iterative fashion, which structure is reminiscent to that of the branches of trees. Most of their properties are due to their terminal functions, which can be easily modified at will to fulfill the desired properties. In particular, many types of catalytic entities have been used as terminal groups of dendrimers. In some cases, a dendritic effect , that is the enhancement of the catalytic properties when a catalyst is linked to a dendrimer, has been observed. It is also generally possible to recover and reuse the dendritic catalysts. The internal structure of dendrimers can also play a key-role, as it manages cavities which can accommodate the catalytic entities, and enable the substrates to interact with them. Catalytic sites included inside the structure of dendrimers are rare, excepted if they constitute the core of dendrimers (or of dendrons, which are dendritic wedges). Effect of the confinement on the catalysis outcome is generally the main aim of these works. Another type of dendritic catalytic entities taking profit of the internal structure concerns metallic nanoparticles used as core of dendrimers. In this chapter, we will gather information about catalytic entities included inside dendrimers, either covalently linked, or noncovalently entrapped, and on their syntheses. The main types of reactions studied, the role of the generation (size) of the dendrimers, their recovery and reuse, and in general the effect of the confinement inside the dendritic structures on the catalytic efficiency will be discussed.

Grignard reagents and Copper

Transition metal-catalyzed cross-coupling reactions involving organic halides or pseudohalides with organometallic Grignard reagents are among the most important method allowing for the C–C bond formation [1–4]. Since their discovery at the beginning of the last century [5], these reactions found a considerable amount of applications in organic synthesis either at the laboratory or at the industrial scale. In fact, the key to the success lied on the association of Grignard reagents with transition metal catalysts which greatly increased their application field. Since the work of Kharasch [6–8], who presented the first studies in this field, a large number of cross-coupling methods involving a variety of transition metal complexes as catalysts have been described. The Kumada-Corriu reaction [9, 10], usually corresponding to the nickelor palladium-catalyzed coupling of electrophiles such as aryl or vinyl halides with Grignard reagents, represents one of the best examples of such a successful combination. Other transition metals are able to promote this reaction and it is also the case, in a general point of view, for the coupling of various families of Grignard reagents with different types of electrophiles which can be catalyzed by Ni-, Pd-, Fe-, Co-, Mn-, Cu-based complexes and to a less extend by Cr-, Zror Ti-based complexes. We will focus in this chapter on copper (Cu)-catalyzed cross-couplings of saturated and unsaturated electrophiles with Grignard reagents.