No abstract

since 1995. He studied in Rennes, where he passed his thesis before a post-doc at MIT (Cambridge) with R. R. Schrock. He is the author, inter alia, of Electron Transfer and Radical Processes in Transition-Metal Chemistry (VCH, 1995, prefaced by Henry Taube) and Chimie Organome ´tallique (EDP Science, 2000). He has been Awarded the Prize of the Coordination Chemistry Division of the French Chemical Society (1981), the German-French Alexander von Humboldt Prize (1989), and the Le Bel Prize of the French Chemical Society (2000). His scientific interests are presently in the field of nanosciences, especially dendrimers, polymers, and colloids, and their applications as sensors, catalysts, and enzyme mimics. Franc ¸oise Chardac (formerly Pisciotti) was born in Poitiers and studied in Bordeaux. She passed her Diplome under the supervision of Professor R. Lalande in terpene chemistry. Then she collaborated with Professor R. Calas and Dr. J. Dunogue `s in organosilicon chemistry in the Laboratoire de Chimie Organique et Organome ´tallique of the University of Bordeaux I, where she is doing a literature search at present.

The appearance of ferrocene in the middle of the 20th century has revolutionized organometallic chemistry and is now providing applications in areas as varied and sometimes initially unexpected as optical and redox devices, battery and other materials, sensing, catalysis, including asymmetric and enantioselective catalysis, and medicine. The author presents here a general, although personal, view of ferrocene's chemistry, properties, functions, and applications through a literature survey involving both historical and up‐to‐date trends and including examples of his group's research in a number of these areas. The review gathers together general features of ferrocene chemistry and representative examples of the salient aspects. Its focus is on ferrocene's basic properties, ferrocene‐containing ligands, the ferrocene/ferricinium redox couple, ferrocene mixed‐valence and average‐valence systems, the ferricinium/ferrocene redox shuttle in catalysis, ligand‐exchange reactions, ferrocene‐containing polymers, ferrocene‐containing structures for cathodic battery and other materials, ferrocenes in supramolecular ensembles, liquid crystals, and nonlinear optical materials, ferrocene‐containing stars and their electrostatic effects, ferrocene‐containing dendrons, dendrimers, and nanoparticles (NPs) and their application in redox sensing and catalysis, and ferrocenes in nanomedicine.

No abstract

The extraordinary development of the design and synthesis of dendrimers has allowed scientists to locate redox sites at precise positions (core, focal points, branching points, termini, cavities) of these perfectly defined macromolecules, which have generation-controlled sizes and topologies matching those of biomolecules. Redox-dendrimer engineering has led to fine modelling studies of electron-transfer metalloproteins, in which the branches of the dendrimers hinder access to the active site in a manner reminiscent of that of the protein. It has also enabled the construction of remarkable catalysts, sensors and printboards, including by sophisticated design of the interface between redox dendrimers and solid-state devices - for example by functionalizing electrodes and other surfaces. Electron-transfer processes between dendrimers and a variety of other molecules hold promising applications in diverse areas that range from bio-engineering to sensing, catalysis and energy materials.

No abstract

Long-term stable 3 nm gold nanoparticles are prepared by a simple reaction between HAuCl4 and sodium borohydride in water under ambient conditions which very efficiently catalyze 4-nitrophenol reduction to 4-nitroaniline.

Catalysis by palladium derivatives is now one of the most important tools in organic synthesis. Whether researchers design palladium nanoparticles (NPs) or nanoparticles occur as palladium complexes decompose, these structures can serve as central precatalysts in common carbon-carbon bond formation. Palladium NPs are also valuable alternatives to molecular catalysts because they do not require costly and toxic ligands. In this Account, we review the role of "homeopathic" palladium catalysts in carbon-carbon coupling reactions. Seminal studies from the groups of Beletskaya, Reetz, and de Vries showed that palladium NPs can catalyze Heck and Suzuki-Miyaura reactions with aryl iodides and, in some cases, aryl bromides at part per million levels. As a result, researchers coined the term "homeopathic" palladium catalysis. Industry has developed large-scale applications of these transformations. In addition, chemists have used Crooks' concept of dendrimer encapsulation to set up efficient nanofilters for Suzuki-Miyaura and selective Heck catalysis, although these transformations required high PdNP loading. With arene-centered, ferrocenyl-terminated dendrimers containing triazolyl ligands in the tethers, we designed several generations of dendrimers to compare their catalytic efficiencies, varied the numbers of Pd atoms in the PdNPs, and examined encapsulation vs stabilization. The catalytic efficiencies achieved "homeopathic" (TON = 540 000) behavior no matter the PdNP size and stabilization type. The TON increased with decreasing the Pd/substrate ratio, which suggested a leaching mechanism. Recently, we showed that water-soluble arene-centered dendrimers with tri(ethylene glycol) (TEG) tethers stabilized PdNPs involving supramolecular dendritic assemblies because of the interpenetration of the TEG branches. Such PdNPs are stable and retain their "homeopathic" catalytic activities for Suzuki-Miyaura reactions for months. (TONs can reach 2.7 × 10(6) at 80 °C for aryl bromides and similar values for aryl iodides at 28 °C.) Sonogashira reactions catalyzed by these PdNPs are quantitative with only 0.01% Pd/mol substrate. Kato's group has reported remarkable catalytic efficiencies for mesoporous catalysts formed by polyamidoamine (PAMAM) dendrimer polymerizations. These and other mesoporous structures could allow for catalyst recycling, with efficiencies approaching the "homeopathic" behavior. In recent examples of Suzuki-Miyaura reactions of aryl chlorides, chemists achieved truly "homeopathic" catalysis when a surfactant such as a tetra-n-butylammonium halide or an imidazolium salt was used in stoichiometric quantities with substrate. These results suggest that the reactive halide anion of the salt attacks the neutral Pd species to form a palladate. In the case of aryl chlorides, the reaction may occur through the difficult, rate-limiting oxidative-addition step.