Our group has introduced and developed ambiphilic compounds combining donor (D) and acceptor (A) coordination sites. Thereby we have very much advance the concept of s-acceptor Z-type ligands and gained more insight into their influence on the electronic, geometric… properties of transition metals. The presence of a Lewis acid moiety in the coordination sphere of transition metals imparts unusual reactivity and opens new possibility for metal/ligand cooperativity. Here, we are particularly interested in cooperative activation of E–H and C–X bonds involving Lewis acid assistance. The ability of Lewis acid sites to act as internal co-catalysts by abstracting a co-ligand at the metal is also of high interest. Besides the coordination, organometallic and catalytic studies, our work includes the design and preparation of new ambiphilic derivatives. In this respect, special attention is devoted to P/B compounds featuring either geometrically-constrained or geometrically-enforced P®B interactions, for applications in metal-free catalysis (such as amine-borane dehydrogenation) and stabilization of highly reactive B species (such as borenium salts and boryl radicals).
2 Chemistry of the coinage metals (G. Szaloki)
Some years ago, our group has initiated a research program aimed at opening new facets in the chemistry of the coinage metals, gold in particular, thanks to ligand design. Fundamental organometallic studies are being performed to identify how we can make gold and its congeners to behave as transition metals. Bifunctional ligands are found to play a major role. Indeed, chelating (P,P) and hemilabile (P,N) ligands emulate fundamental yet hitherto unknown reactivity such as oxidative addition, migratory insertion, b-H elimination… In addition, special interest is devoted to complexes featuring unusual bonding situations such as s and p gold complexes (relevant to C–H activation processes), reactive carbene complexes of gold (either electrophilic or nucleophilic), H-bonded complexes… The new ligand sets and reactivity paths also open new opportunities in catalysis, and an important body of work is achieved in this direction. Representative examples are the hydroarylation of alkynes with new cyclometalated Au(III) complexes and the regioselective arylation of indoles via Au(I)/Au(III) catalysis.
3 Pincer complexes, Non-innocent ligands and Cooperative catalysis (B. Martin-Vaca, J. Monot)
Over the last decade, the chemistry of pincer complexes has tremendously progressed. These complexes are characterized by the meridional coordination of a tridentate ligand and benefit from a unique balance between stability and reactivity. In this context, we have developed an original family based on the indene skeleton that can adopt for the first time in plane η1-coordination. The high electronic density of the indenyl backbone, especially over C1 and C3, confers a basic/nucleophilic character to the ligand and allows active participation in chemical transformations. Thus, the ligand is able to contribute to the activation of Y‒H bonds with Y = O, N, C (metal / ligand cooperativity). We exploited it in cooperative metal / ligand catalysis for highly atom-economic reactions such as alkynoic acid / alkynylamide cycloisomerization, carboxylative cyclization of propargylamines and the Conia-ene reaction.
4 Biodegradables polymers : synthesis and applications (B. Martin-Vaca)
Synthetic biodegradable polymers, polyesters and polycarbonates in particular, have attracted considerable interest over the last decades not only for the encapsulation and sustained release of drugs, but also for commodity applications as well as microelectronics (nanolithography). Among the preparation processes of these polymers, the ring-opening polymerization (ROP) of cyclic monomers allows good control of the polymer structure. In this context, we are developing original and efficient approaches for the controlled preparation of well-defined biodegradable polymers under mild conditions. Our work combines different aspects: (i) the development of new organic and/or metallic catalytic systems, including dual organic/metallic catalytic systems, (ii) the synthesis of functionalized monomers, (iii) the preparation of (co)polymer of controlled architectures.
We have demonstrated the efficiency of sulfonic, phosphoric and phosphoramidic acids for the controlled polymerization of lactide, ε-caprolactone and trimethylene carbonate. In addition, we have succeeded in the development of new catalytic systems combining a Brönsted base (such as an amine or a phosphine) and a metal-based Lewis acid (such as Zn or In derivatives) for the synthesis of linear and cyclic polyesters. We are very interested in understanding the mode of action of the new catalysts and the polymerization mechanism. We also seek to apply the new catalytic systems to the preparation of well-defined block copolymers capable to self-segregate at the nano-scale, as well as random copolymers bearing lateral functional groups, to finely tune the polymer properties.