Mathieu J.-L. Tschan

Synthesis of biodegradable polymers from renewable resources

The vast majority of commodity materials are obtained from fossil fuels. However, many studies predict that all fossil resources will be depleted within a few centuries. Biomass represents an abundant carbon-neutral renewable resource for the production of materials. Using biomass for the production of new polymers can have both economic and environmental benefits. This review focuses on the use of biomass for the synthesis of biodegradable polymers.

Zinc and cobalt complexes based on tripodal ligands: synthesis, structure and reactivity toward lactide.

The coordination chemistry of a series of pro-ligands ([L¹]-[L⁶]) with cobalt and zinc derivatives has been studied. All complexes have been characterized by multinuclear NMR, elemental analysis, and by single-crystal X-ray diffraction studies. Polymerization of rac-lactide takes place at 130 °C in the presence of cobalt and zinc complexes to yield polymers under solvent free conditions with controlled molecular masses and narrow polydispersities.

Yttrium catalysts for syndioselective β-butyrolactone polymerization: on the origin of ligand-induced stereoselectivity

Synthesis of aliphatic polyesters has been studied intensively due to their biocompatible and biodegradable properties and their applications in medical and agricultural fields. Among them, polyhydroxybutyrate (PHB), which is a naturally occurring polymer, is synthesized by a variety of bacteria and algae. However, this polymer has poor mechanical properties due to its brittleness. Herein is presented a practical route to a highly syndiotactic PHB by way of a one-pot reaction. We report the results of a comprehensive investigation of the newly discovered stereoselective and controlled polymerization of racemic β-butyrolactone (rac-BBL) using an initiator prepared in situ from yttrium(III) isopropoxide Y(OiPr)3, and a bisphenoxide ligand. DFT studies on the alkoxide catalyst reveal that the R and S monomers are almost equivalent for the first ring-opening reaction. The selectivity of the next insertion was scrutinized, demonstrating that the polymerization process is predicted to be stationary (back-side insertion).

Supported neodymium catalysts for MMA polymerization: on the origin of surface-induced stereoselectivity

The polymerization of MMA by a supported neodymium borohydride catalyst proceeds with moderate tendency toward isoselectivity, whereas the molecular precursor generates a syndiotactic-rich polymer. DFT studies reveal that initiation proceeds via borohydride attack on the first coordinated monomer followed by BH3 trapping by the silica surface. The selectivity of the next two insertions was scrutinized, demonstrating that interactions between the growing chains oxygens and the metal enforce conformations that lead to favoured formation of an isotactic polymer chain.

Enantioselective hydrogenation of ketones by iridium nanoparticles ligated with chiral secondary phosphine oxides

Chiral iridium nanoparticles (IrNPs) were synthesized by H2 reduction of (1,5-cyclooctadiene)(methoxy)iridium(I) dimer ([Ir(OMe)(COD)]2) in the presence of an asymmetric secondary phosphine oxide (4,5-dihydro-3H-dinaphtho[2,1-c:1′,2′-e] phosphepine-4-oxide, L). This highly reproducible and simple procedure furnished small, well dispersed and soluble nanoparticles of 1.4 (0.2) nm, which were found to be active catalysts for the enantioselective hydrogenation of prochiral ketones. This study represents the first example of asymmetric hydrogenation catalyzed by SPO-ligated metal nanoparticles and also the first example of asymmetric hydrogenation catalyzed by non-supported chiral IrNPs. The IrNPs were characterized by the use of a wide variety of techniques, such as TEM, HRTEM, EDX, XPS, ATR FT-IR, ECD, and MAS-NMR spectroscopy with and without 1H–13C cross-polarization (CP).

Ruthenium Metal Nanoparticles in Hydrogenation: Influence of Phosphorus-Ligands

Ruthenium nanoparticles (RuNPs) attracted much attention in the last decade because of their potential applications in catalytic hydrogenation and oxidation reactions. The broad spectrum of applications of ruthenium in catalysis, notably together with its relatively low price, renders RuNPs an attractive alternative to platinum or rhodium. Many different additives were reported for the stabilization of RuNPs, in particular polymers and ionic liquids. Lately, many reports showed the effectiveness of RuNPs stabilization by coordinating molecules commonly used in organometallic chemistry such as amines, thiols, and alcohols. Very recently, the type of stabilizers was extended to more sophisticated ligands such as phosphorus, nitrogen and carbon donor ligands. In this mini-review, we will present an overview of the various ligands used for RuNPs, with an emphasis on phosphine ligand effects on the morphology and catalytic activity in hydrogenation reactions. Appendix gives a tabular overview of the key features of the RuNPs reviewed.

Telomerisation of Buta‐1,3‐diene and Methanol: Superiority of Chromanyl‐Type Phosphines in the Dow Process for the Industrial Production of 1‐MOD

Butadiene and methanol were telomerised in the presence of palladium catalysts with ligands containing 8-diphenylphosphinochromane-like substituents at phosphorus. MonoXantphos and monoSPANphos afforded the most active, stable and selective catalysts known to date under commercially relevant production conditions for 1-methoxyocta-2,7-diene, the precursor to oct-1-ene.

A joint experimental/theoretical investigation of the MMA polymerization initiated by yttrium phenoxyamine complexes

A joint experimental/theoretical study has been carried out on the putative MMA polymerization catalyzed by an yttrium isopropyloxide complex. Despite its high activity in lactone polymerization, this catalyst is found to be unreactive on methyl methacrylate (MMA) polymerization. This surprising result is rationalized using a computational approach at the DFT level. Indeed, the endothermicity of the initiation step explains this lack of reactivity. The theoretical proposal of yttrium amido complexes as catalysts allows overcoming this initiation problem.