Sébastien Delfosse

Ruthenium catalysts bearing N-heterocyclic carbene ligands in atom transfer radical reactions

The catalytic activity of ruthenium-p-cymene complexes bearing N-heterocyclic carbene ligands in atom transfer radical addition (ATRA) or polymerisation (ATRP) strongly depends on the substituents of the carbene ligand, thereby providing a nice illustration of the importance of organometallic engineering and ligand fine tuning in homogeneous catalysis.

Olefin cyclopropanation catalysed by half-sandwich ruthenium complexes

Abstract Ruthenium complexes of the type [RuX(Cp′)(PPh 3 ) 2 ] (X=Cl and H; Cp′=Cp, Cp*, indenyl, and carboranyl) efficiently catalyse olefin cyclopropanation with diazoesters, and the cis / trans stereoselectivity of the resulting cyclopropanes strongly depends on the Cp′ ligand. With [RuCl(Cp*)(PAr 3 ) 2 ] complexes, cyclopropanation competes with the formal carbene insertion into C–H vinyl bonds of styrene, whereas ring-opening metathesis polymerisation takes place with norbornene, lending support to the formation of ruthenium–carbene and ruthenacyclobutanes as intermediates in these reactions.

Microwave-Assisted Ruthenium-Catalyzed Reactions

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers has been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared with conventional heating methods. The present contribution aims at illustrating the advantages of this technology in homogeneous catalysis by ruthenium complexes and, when data are available, at comparing microwave-heated and conventionally heated experiments. Selected examples refer to olefin metathesis, isomerization reactions, 1,3-dipolar cycloadditions, atom transfer radical reactions, transfer hydrogenation reactions, and H/D exchange reactions.

Half-sandwich ruthenium complexes for the controlled radical polymerisation of vinyl monomers

Abstract Ruthenium complexes of the type [RuX(Cp # )(PPh 3 ) 2 ] (X=Cl and H; Cp # =Cp, Cp*, indenyl, and carboranyl) catalyse the radical polymerisation of styrene and n -butyl acrylate, and both the catalyst activity and the degree of control of the polymerisation strongly depend on the Cp # ligand and the monomer.

Tuning of ruthenium N-heterocyclic carbene catalysts for ATRP

Depending on the substituents, R1 and R2, ruthenium(II)–p-cymene complexes bearing N-heterocyclic carbene ligands are either efficient catalysts for the well-controlled atom transfer radical polymerisation of methyl methacrylate and styrene, or promote a redox-initiated free-radical process.

Dual Activity of Ruthenium Catalysts in Controlled Radical Reactions and Olefin Metathesis

The formation of carbon-carbon bonds using free radicals is of utmost importance both in synthetic organic chemistry and in polymer chemistry [1]. The developments that took place during the last decade have considerably modified the view that free radical reactions are commonly uncontrollable. Catalytic systems are now available, that allow radical reactions to be carried out in a precise and controlled manner. In particular, the past few years have witnessed a rapid growth in the development and understanding of controlled radical reactions based on the combination of suitable radical initiators and of transition-metal complexes. For instance, the addition of a polyhalogenated alkane to an olefin, also known as the Kharasch reaction [2], has largely benefited from the replacement of classical radical initiators such as peroxides or UV light by transition- metal complexes that promote a single-electron transfer or a redox-based chain reaction. The latter process is usually referred to as an Atom Transfer Radical Addition (ATRA). In the presence of a high ratio of olefin compared to the halogen derivative, successive insertions of the unsaturated monomer lead to a macromolecular chain, and the net process is known as an Atom Transfer Radical Polymerization (ATRP) (Scheme 1). Among the metals used for promoting ATRP, copper, nickel, iron, and ruthenium tend to display the highest activities, but complexes of rhenium, rhodium, and palladium have also been employed [[3],[4]].

Microwave-Assisted Olefin Metathesis

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers have been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared to conventional heating methods. The present contribution aims at illustrating the advantages of this technology in olefin metathesis and, when data are available, at comparing microwave-heated and conventionally heated experiments

Synthesis of New Macromolecular Architectures Based on Ring Opening Metathesis Polymerisation and Atom Transfer Radical Polymerisation

Thanks to recent advances in the chemistry of preparing polymers, an increasing number of tools are at our disposal for the design of polymer materials. The design level ranges from monomer synthesis, controlled stepwise or chainwise polymerisation, block copolymer synthesis, branching and crosslinking reactions. Depending on the structure of the individual polymer chains formed, these will be organised in the bulk to give specific properties. Hence, this gives us two architectural levels: the structure of individual macromolecules and the microstructure of the material produced. The synthesis of properly tailored macromolecular architectures [1] can be achieved by using living/controlled polymerisation processes such as anionic [2], cationic [3], radical [4] or group transfer polymerisation [5], ring-opening polymerisation of lactones and lactides [6], ring-opening metathesis polymerisation (ROMP) of cyclic olefins [7-9], and co-ordination polymerisation [10]. Of particular interest today is the combination of two of these processes. The present chapter aims at reviewing the synthetic routes developed recently for building up novel (co)polymer structures based on ROMP and atom transfer radical polymerisation (ATRP), with a special emphasis on the combination of two living/controlled polymerisation techniques.